Karine Aillerie
email: karine.aillerie@reseau-canope.fr

Sarah Mcnicol
email: mcnicol@mmu.ac.uk

Are Social Networking Sites information sources? : Informational purposes of high-school students in using SNS

Keywords: Social media, Social networking sites, Information seeking, Teenagers, Information literacy, Transliteracy, information grounds Social media, Social networking sites, Information seeking, Teenagers, Information literacy, Transliteracy, information grounds

Although social networking sites (SNSs), such as Facebook or Twitter, are widely used by teenagers, to date, research has focused on the social uses of SNSs. This research sought to investigate the ways in which high school students (15-19 years) use SNSs in order to find information. It highlights the importance of considering how young people may use SNSs for everyday life information as well as for academic and school oriented information. Findings from a web-based survey of students from the UK, France, Thailand and Denmark show that SNSs are information sources for most teenagers, especially for information related to social activities. Although academic information seeking were not among the most common reasons for using SNSs, the findings indicate that many students do use SNSs for such purposes, as well as everyday life information seeking.

Introduction

SNSs (social networking sites) are defined by boyd and Ellison (2008: 211) as "web-based services that allow individuals to (1) construct a public or semi-public profile within a bounded system, (2) articulate a list of other users with whom they share a connection, and (3) view and traverse their list of connections and those made by others within the system". The expanding growth of SNSs has meant that they have become a daily activity for millions of people and especially for teenagers (Hampton et al, 2011;Bigot and Croutte, 2014;EU kids online, 2014;[START_REF] Lenhart | Teen, Social Media and Technology Overview[END_REF]. While the term 'social media' encompasses a wider range of services, such as blogs, collaborative projects and collaborative social worlds (Kaplan and Haenlein, 2010), in everyday discussions the two terms are often used interchangeably. Although Facebook is still the most widely used SNS, teenagers now tend to embrace newer social networks such as Instagram, WhatsApp or Snapchat [START_REF] Duggan | Social Media Update 2014[END_REF]. Many studies describe these teenagers' uses of SNS, mainly from social sciences and psychology viewpoints. For the most part, such studies focus on communication and social uses of SNS, aiming to describe the nature and processes of a "digital sociability" [START_REF] Cardon | La production de soi comme technique relationnelle : Un essai de typologie des blogs par leurs publics[END_REF] and then to warn about the potential dangers and the necessity to protect privacy and personal data [START_REF] Livingstone | Taking risky opportunities in youthful content creation: teenagers' use of social networking sites for intimacy, privacy and self-expression[END_REF]Ito et al, 2010).

Apart from individuals, many brands, companies, organizations, public institutions (local national as well as international level), and both traditional and citizen-based media make use of SNSs, having a public Facebook page, a Twitter account, Youtube channel among others. SNSs thereby provide a huge amount of information, as well as different types of information compared to those available from many other sources, and covering a wide range of topics. SNSs can, therefore, be considered as effective hubs through which information flows, as is demonstrated in the recent agreement, called « Instant Articles », between Facebook and nine press publishers to submit articles directly to its members. As information providers, SNS have been shown to play an important role in participation and political engagement. Recent history has demonstrated that these communication platforms allow people to challenge the establishment by publishing and sharing anti-establishment views or opposing debates, and facilitate people gathering to demonstrate commitment, or even for strikes or riots [START_REF] Shirazi | Social media and the social movements in the Middle East and North Africa: A Critical Discourse Analysis[END_REF]. Furthermore, recent works point out that SNSs could be used as direct information sources explicitly by students (Kyung-Sun et al, 2011, 2014;[START_REF] Bae | Why People Use Social Networking Sites[END_REF][START_REF] Willemse | JAMES -Jeunes, activités, médias: enquête Suisse[END_REF]. This is not surprising given the availability, and increasingly popularity, of user generated content. Moreover, many young people, and most information searchers in general, rely on sources easily accessible even though the trustworthiness of information is questionable [START_REF] Flanagin | Kids and Credibility: An empirical examination of youth, digital media use, and information credibility[END_REF][START_REF] Biddix | Convenience or credibility? A study of college student online research behaviors[END_REF].

In this paper, we consider whether teenagers (15)(16)(17)(18)(19) use SNSs to access and/or seek information. Then we investigate the possible SNS information practices of teenagers and explore what kind of information they might look for on SNS. Information related to everyday life as well as academic works or school life are considered.

These questions highlight important issues: in the first place, specific uses of the Internet and Web 2.0 by teenagers questions the evolution of information practices of future citizens. Furthermore, the capability to search, evaluate and share information in a collaborative setting, is presented as a crucial skill domain in many Information Literacy (IL) curricula (e.g. Advisory Committee on Information Literacy, 2011;ACRL, 2015) and, chiefly, in renewed paradigms and frameworks such as Transliteracy [START_REF] Thomas | Transliteracy: Crossing divides[END_REF] or Metaliteracy [START_REF] Mackey | Metaliteracy: Reinventing information literacy to empower learners[END_REF]. Indeed, while IL guidelines are usually focused on individual skills and individual assessment, the key competencies have an increasingly collective dimension: sharing information with friends and with a large and unknown audience and evaluating information created by multiple participants for example. As Mackey and Jacobson (2014: 309), authors of the Metaliteracy framework, point out, the challenge for teachers and trainers is to define specific competencies for printbased information as well as decentered networks: "In many ways social media is ideally suited for research if we recognize these collaborative spaces as a means for effectively creating and sharing knowledge in diverse modes, and not just informal social interactions". However the situation at school is that, broadly speaking, media, and especially web-based media and social networks, are perceived as threats for children and teenagers rather than as resources to support teaching or learning. In an approach that is arguably inconsistent with the reality of teenagers' digital habits, SNSs are often prohibited by school policies and dismissed as games or 'kids' stuff' at best, clearly differentiated from serious work that is done at school. This can contribute to the "participation gap" mentioned by Jenkins and colleagues (2009). And, if SNS may be meaningful information sources for young people, researchers and educators need to better understand these SNS-based information processes in order to design appropriate evaluation guidelines. This research is intended as a first, explorative step that should be extended in order to continue to test and specify the ideas and findings presented here.

SNSs and information seeking

As indicated in introduction, general research about teenagers' information practices seldom includes SNSs as information sources. However, research about the needs that SNSs satisfy for people does include information seeking [START_REF] Whiting | Why people use social media: a uses and gratifications approach[END_REF]. Indeed, from a research point of view the different reasons to refer to a SNS need to be better understood because, to date, the social motivations have chiefly been emphasized. Some researchers have investigated SNSs specifically as information sources. In Norway, Petter Bae Brandtzaeg and Jan Heim (2009) carried a qualitative survey (1200 responses) in 2007 on social networking site users (aged from 16 to 29). The authors demonstrated that information needs were listed by participants (10%, n=220): « Users reporting access to information, including about fashion, music, literature, cultural events, current happenings in their neighborhood and access to new and shared knowledge regarding people's opinions related to everything from politics and to more tedious matters.

Information updates are related to: a) Friends; b)Neighborhood; c) City events; d) Fashion; e) Music; f) Happenings; g) Help with homework at school f) interests/hobbies; g) other and more customized forms of information than on TV and radio" (Brandtzaeg and Heim, 2009:148). They suggested that the category named "debating" (6.5%, n=143) can be integrate the information category, "because debating often takes place in order to gain access to new information through a collaborative discussion process" (Brandtzaeg and Heim 2009, p.148). Although this survey did not focus especially on teenagers, participants cited academic homework as a motivation to seek information on SNSs.

Other researchers who are also primarily concerned with identifying the main motivations that lead people to use SNSs include [START_REF] Grant | Young peoples' relationships with online marketing practices: an intrusion too far[END_REF] who isolated key motivations that lead teenagers (13)(14)(15)(16)(17) in particular to use SNS including information seeking "(…) to enhance their mood, learn by experience, as a form of passive escapism, as social interaction, and to find or give information and advice" (cited by Jansen et al, 2011:121). Some of the most significant studies that demonstrate the use of SNS as direct information source concern undergraduate students such as the several studies conducted by research team led by Kyung-Sun Kim. Kim and colleagues (2011) carried out a first online questionnaire that aimed to investigate what kinds of SNSs are used as information sources and why they are used by undergraduate students from a public university (446 participants). This study also examined what kinds of actions users take in order to evaluate the trustworthiness of information provided by social sources. The study found that Wikipedia was the most widely used source (98%) while SNSs such as Facebook, MySpace and LinkedIn were also used as information sources (97%), followed by online user reviews (72%), YouTube (53%) and Q&A sites (e.g. Yahoo! Answers) (53%), blogs (32%) and microblogs such as Twitter (24%). The authors concluded that a range of SNSs and social media are used for everyday life information seeking while some are used for both everyday life information and academic purposes (Wikipedia, YouTube, Q&A sites). Furthermore, this study shows that different sites are used for different purposes: Wikipedia was used mainly for getting background/introductory information and a quick overview, while sites like Facebook were used mainly for keeping in touch with others, getting updates/news and for getting others' opinions. User review sites were used for getting others' opinions/comments on products and help with purchase decisions. YouTube was used for recreational information and for finding solutions to a problem or how-to instructions, while for problem-solving, Q&A sites were also used often [START_REF] Kim | Social Media as Information Source: Undergraduates' Use and Evaluation Behavior[END_REF].2).

Kyung-Sun Kim and other colleagues conducted additional studies (Kim et al, 2013;Kim et al, 2014;Kim and Sin, 2014). The 2013 study involved 1286 students from a public university filling out a web based survey. Findings showed that sources used by students for information seeking related to academic purposes were, firstly, wikis, followed by blogs, social Q&A, media-sharing sites, and forums. In 2014, two further surveys were launched to collect data via a web-based survey with 809 undergraduate students (Kim et al, 2014) and web-based survey plus focus groups from 1355 students in US and 194 in Singapore (Kim and Sin, 2014). Findings of the first study showed that most of the SNSs and social media platforms are used as information sources, and wikis, user reviews, and media-sharing sites emerged as the top platforms. Results also revealed differences in the frequency of information seeking and in the purpose of use depending on gender, class level, academic discipline and Big Five personality traits [START_REF] Mccrae | Validation of the five-factor model of personality across instruments and observers[END_REF]. In the second study, little difference was found between the two countries, while different platforms seemed to be used depending on different contexts. Q&A sites and forums tended to be used in the academic context. SNSs, user reviews, and microblogs were used in the everyday life situations, while wikis and media-sharing services were most often used in both contexts.

Recently, the JAMES (Jeunes Activités Médias) study shed light on teenagers' information seeking on SNSs [START_REF] Willemse | JAMES -Jeunes, activités, médias: enquête Suisse[END_REF]. Since 2010, this representative study has examined the use of media by young people in Switzerland every two years. In 2014, 1086 young people (age from 12 to 19) were interviewed. This study showed that SNS are an important information channel for them: SNSs were in third position, after videos sharing websites and search engines, with 78% (n = 854) consulting them every day or several times a week. Indeed, for the 2014 session, video sharing websites such as Youtube have been included in the survey as an information channel. The participants declared that this kind of sites is not useful for leisure exclusively but for information seeking as well. This study also demonstrated a greater tendency for girls to seek information through SNSs.

These findings are disputed slightly by other results however. For instance, Williamson and colleagues (2012) interviewed 34 Australian students (age 18 to 25) about their topics and sources when seeking information in everyday life information seeking situations. This study did not focus especially on SNSs.

These results suggest that print media such as books and newspapers still played an important role for young people while SNSs were perceived as important for interaction with friends rather than for news gathering.

Although Facebook, could be used to get some types of news e.g. about friends or sport, it was still mostly used for communication. To explain this reluctance to use SNS as an information source, participants described their skeptical feelings about privacy issues and quality of information provided on line and especially via SNSs. Nevertheless, this study emphasized the wide range of media that young people use to meet their information needs.

Research questions

As this literature review demonstrates, relatively few studies exist on our topic: teenagers' information seeking on SNS. Furthermore, all the cited studies point to a lack of research on this theme and at the same time emphasize the issues that this raises. a. As [START_REF] Kim | Social Media as Information Sources: Use and Evaluation of Information from Social Media[END_REF] argue: "An empirical study is urgently needed to better understand how users evaluate and use the information from these social media, and to provide help for the effective use of such sources". Based on the insights gained from the above discussion of the literature, the following research questions will be investigated in this paper:

In the context of "Web 2.0", what does the information landscape of teenagers now look like? More specifically, do they use SNSs as information sources? What are their motivations for using SNSs specifically as information sources? Do they use SNSs as information sources for everyday life topics alone, or do they use SNSs as information sources for academic purposes as well?

Theoretical background

 Everyday life information seeking

The uses of SNSs by teenagers are directly concerned with the sphere of everyday life. As we have emphasized in the introduction, these uses are little studied by the research into formal settings such as the school and workplace, but as incursions, disturbances, untimely emergence of intimacy. This subdivision between "formal" settings of information seeking (work and school) and "informal" settings of information seeking (everyday life and leisure) reinforces the traditional partition of the information seeking research into two spheres of life experience: work or job related on one hand; non-work or everyday life on the other. This distinction was evident in both theoretical and methodological claims against the lack of scientific studies about everyday life information seeking compared to studies about information seeking for work purposes in the 1980s. This led several authors to propose models of ELIS (everyday life information seeking). The model proposed by Reijo [START_REF] Savolainen | Everyday life information seeking: Approaching information seeking in the context of "way of life[END_REF] from the Finnish university of Tampere is perhaps the best known and aims to initiate a concept able to highlight the "legitimate nature of non-work contexts" (p.266).This founding publication revealed the place of information in daily life and the diversity of relations people have with the media, which is an appropriate basis for a study focused on SNSs. Savolainen (1995: 266) stressed that the concept of ELIS is "residual by nature", meaning that it is difficult to separate completely the two contexts (professional on one side, and daily life on the other), and that the different contexts in which an individual life takes place are not fully separated from the individual's point of view. Moreover, in the 20 years since its publication, features enabled by connected devices, such as mobile phones, have substantially evolved. It could therefore seem useful to reread the concept of ELIS in light of recent research, on mobility. Indeed, Stefana [START_REF] Broadbent | Intimacy at Work: how digital media bring private life to the workplace[END_REF] showed how much information and communication technology transforms public and institutional spaces as a consequence of the extension of the personal and intimate sphere outside of private spaces. What were clearly distinct contexts at earlier points in history are today geographically and temporally mixed. [START_REF] Savolainen | Everyday life information seeking: Approaching information seeking in the context of "way of life[END_REF] highlights the potential passive nature of the informational practice. This finding echoes the practice of social networks based on a connection and constant attention to the notification system and continuous scrolling of updates. Moreover, Savolainen's model, as well as the other ELIS models, identify people (personal networks, family and friends) as the most easily accessible sources of information, even for information acquired by chance [START_REF] Williamson | Discovered by chance: The role of incidental information acquisition in an ecological model of information use[END_REF][START_REF] Mckenzie | A model of information practices in accounts of everyday-life information seeking[END_REF], and mass media and institutional sources as less accessible sources of information. In line with the ELIS perspective, [START_REF] Agosto | Toward a Model of the Everyday Life Information Needs of Urban Teenagers, Part 1: Theoretical Model[END_REF] carried out a qualitative survey in order to determine the sources or channels US urban teenagers consult when engaging in everyday life information seeking and their most frequent everyday life information needs. As a result of this survey, authors found that the participants indicated a preference for friends and family as information sources for their everyday life information seeking. This is an appropriate basis for research on SNSs as information sources for teenagers because SNSs are typically human sources as they are maintained by individuals.

 Information grounds

The concept of « information grounds » developed by Karen Fisher (formerly Pettigrew) is relevant to understand the information environment of people. She conceived the notion as "an environment temporarily created by the behavior of people who have come together to perform a given task, but from which emerges a social atmosphere that fosters the spontaneous and serendipitous sharing of information" (Pettigrew: 1999: 801). We choose to refer to this concept as it highlights the crucial role of human relationship and social interactions in the informational process [START_REF] Fisher | Information grounds and the use of need-based services by immigrants in Queens, New York: a context-based outcome evaluation approach[END_REF].

Information grounds theory focuses on informal social settings "ranging from book clubs, gyms, folk festivals and bus stops to hair salons and supermarket queues" (Counts and Fisher, 2010: 99). But information grounds research points out that the main information grounds that people have are the workplace, the activity groups (linked to leisure or sport, playgrounds, clubs etc.) and places of worship. It is noteworthy that for these authors, the information needs are determined by tasks directly deducted from the professional roles. This raises questions about the role of academic setting and associated tasks in the information processes of teenagers. While the concept of information grounds does not initially include the formal context of school, it seems relevant to think that this context plays a significant role in the information sharing processes.

 Transliteracy

Nowadays people have to deal with a wide range of existing information sources (websites, blogs, human sources, books and magazines, booklets, media, TV, radio etc.). The concept of information literacy itself is being redefined in the light of the developing "mediascape" [START_REF] Appadurai | Disjuncture and Difference in the Global Cultural Economy[END_REF]) as well as its uses. A strong theoretical and methodological paradigm is hence emerging that features a "meta skill" relevant to the presented study: "Transliteracy". A definition of this concept is given by Sue Thomas and colleagues (2007):

"Transliteracy is the ability to read, write and interact across a range of platforms, tools and media from signing and orality through handwriting, print, TV, radio and film, to digital social networks". Transliteracy emphasizes the need to work at a global level of expertise that takes into account the various media and all kind of literacies (Ipri 2010) rather than limiting activities to specific literacies, especially digital ones. In addition, the concept and research programme of Transliteracy oblige us to encompass multiple kind of motivations to use SNSs rather than the only one: the socialization aspect. As a part of the current information landscape, SNSs should be taken into account when information culture is being defined. Furthermore, as is the case with SNSs, the concept of Transliteracy attaches great importance to the human interaction within information seeking and sharing processes.

Methodology

In order to collect data on users' characteristics and their possible use of SNS as information sources, a study was conducted using a short online questionnaire (10 questions) developed using Google Forms. This was developed in French and translated into English and Danish. The initial questions aimed to gather basic demographic information (age, gender, course studied). Participants were then asked about their general use of SNS (number of accounts, type of SNS) and their information uses of SNS (type of SNS used to seek information, frequency, topics sought, content shared or published on SNS). Regarding the topics sought, we predefined 13 categories from the literature review and from two pretest interviews of the questionnaire.

Data were collected between December 2014 and April 2015. A link to the survey was sent to librarians and teachers via email lists (e.g. CDI-DOC mailing list, School-Library-Research and LIS-Info-Skills JISCMAIL lists); professional associations (e.g. the UK School Library Association (SLA); and personal contacts of the authors). Those interested in participating were asked to send the survey link to any students they taught aged between 15 and 19. The data were downloaded from Google Forms as an Excel spreadsheet, and then imported into SPSS where the responses were analyzed. Descriptive statistics were generated for all the questions and chi-squared analysis conducted for investigated differences between gender categories of respondents.

In total, 473 responses were received: 64.5% were from female students and 35.5% from male students. The majority of students (94.3%) were aged between 15 and 18. 65.8% of responses were from students in the UK, 22.0% from France; 5.7% from Thailand; and 5.1% from Denmark. There were also a non-significant number of responses from students in other non-European countries (Namibia, Netherlands, Philippines, Qatar, Singapore and Russia).

A companion survey was also conducted in Chile for which results will be published separately (forthcoming).

Findings

Setting the scene: respondents' general uses of SNSs

Social networks high-school students have accounts for

As Table 1 shows, the most common SNSs students had accounts for were Facebook (92.9% had an account), YouTube (76.0%) and Snapchat (75.1%). Students were least likely to have accounts for Flickr (2.3%), Ask.fm (15.4%) and Vine (17.7%).

Table 1: Which SNSs do you have an account for? (n=473)

Other sites mentioned by small numbers of students include Pinterest, WeChat, DeviantArt, BuzzFeed, Reddit, StumbleUpon, Instapray, Meow Chat, Viber, Twitch, 9GAG and Skype.

There were some differences between SNSs male and female students had accounts for. There was strong evidence that female students surveyed were more likely to have an account for Instagram (F=63.3%; M=36.9%; p<0.01), WhatsApp (F=39.7%; M=25.6%; p<0.05) and Tumblr (F=38.7%; M=18.5%; p<0.01) and there was also some evidence that they were more likely to have an account for Snapchat (F=78.0%; M=67.3%; p<0.05). However, there was greater use of Google+ (F=47.2%; M=63.1%; p<0.01) and YouTube (F=71.5%; M=83.3%; p<0.01) amongst male students.

Social networking sites students use most regularly in general

Facebook was, overwhelmingly, the most commonly used SNS (77.4% said they used it regularly), as shown in Table 2. Snapchat (33.2%) and Instagram (29.2%) were next, followed by YouTube (27.3%) and Twitter (22.6%). The proportion of account holders who considered themselves regular users ranged between 83.0% for Facebook to 2.4% for Google+. However, only 1.9% of students surveyed did not use any SNSs regularly.

Table 2: What social networking sites do you use most regularly in general? (n=473)

Other SNSs mentioned by less than five students included Skype, Reddit, Pinterest, Vine and Soundcloud. More than half the students (55.8%) used SNS to seek information regularly and almost a further quarter (23.7%) did so occasionally. Just less than a fifth (18.8 %) rarely or never used SNS to seek information (see Figure 1). A few indicated in their responses that they felt the idea of doing so was ridiculous.

Do the participants use SNSs as information sources?

How often students use social networking sites are used to seek information

Social networking sites students use most regularly to search for information

When students were asked about SNSs used to search for information, again, Facebook was the site used most regularly (39.1%), as shown in Table 3. YouTube was used regularly to search for information by 30.2% of students and Twitter by 20.0%. All other SNSs were used regularly to search for information by less than 10% of students. The popular general sites, Instagram and Snapchat were used by just 3.8% and 0.8% respectively for information purposes.

Table 3: What social networking sites do you use most regularly to search for information? (n=473)

The number of students regularly using specific SNSs to search for information was less than the number using the same SNSs for general purposes, with the exception of Google+, Reddit and Pinterest which were mentioned more frequency as sites used regularly for information purposes. A little over half the number of students who used Facebook regularly in general used it regularly specifically to search for information, but more than four-fifths of the number using Twitter and YouTube in general used them specifically to search for information. Information related to friends was the most common type of information students looked for on SNSs (69.8%). This was followed by information about cultural events (56.0%) and international news (49.3%) 1 .

What are participants' motivations for using SNSs specifically as information sources?to

Kinds of information students sought on social sites

Information related to health (14.8%) and practical information (17.5%) were the least commonly sought types of information (see Figure 2). There were some, mostly not unexpected, gender differences in the types of information sought via SNSs. Male students were more likely to look for sports news (F=11.8%; M=33.3%; p<0.01) and games-related information (F=10.8%; M=47.6%; p<0.01), while female students were more likely to use SNSs for information about fashion and beauty (F=42.3%; M=5.4%; p<0.01).

Female students were also most likely to uses SNSs to find information about friends (F=77.4%; M=56.0%; p<0.01) and cultural events (F=60.0%; M=48.8%; p<0.05). 1 The percentage searching for national news may be slightly lower than expected as international responses to the English version were not anticipated at the survey launch, so mention of the UK in the description of this item may have been misleading for overseas students.

While tasks directly related to education and school were not amongst the most common reasons for using for information purposes, neither were they at the bottom of the list. More than one-quarter of students (27.7%) said they used SNSs to find information for a task at the direction of a teacher and one-fifth (20.3%) used SNSs to find information for a school project independently (i.e. not explicitly directed teacher).

Around the same percentage (20.1%) said they had used SNSs to find additional information about topics taught in class. In addition, just over one-fifth (22.4%) used SNSs to search for information related to educational and vocational guidance. There were no significant gender differences in the use of SNSs for obviously school-related tasks.

Other types of information mentioned by small numbers of students included travel and geography; cookery;

'how to' videos; information about music and films; political and activist information; and information about hobbies.

Satisfaction with the quality and reliability of information found on SNSs

When asked how often they were satisfied with the quality and reliability of information they found on SNSs, students' responses were skewed towards the positive end of the scale, although just 5.1% said they were always satisfied (Figure 3). The information on SNS clearly has some value for most students, although they are conscious it needs to be treated with caution. There was a gender difference between the levels of satisfaction expressed by male and female students (p<0.01), with boys more likely to express more extreme opinions while girls were more moderate and more likely to select the middle option.

Do you publish information on SNSs?

Only 16.5% of students said they did not publish any information on SNSs. There was a statistically significant difference between boys and girls in response to this question with boys being less likely to publish information on SNSs (F=11.1%; M=26.2%; p<0.01). Personal photos or videos were the most common form of publishing information on SNS (67.2%), especially amongst female students (F=75.7%; M=51.8%; p<0.01). This was followed by publishing comments and opinions (63.6%). Around one-quarter of students said they published academic information such as class Facebook groups (27.7%) and similar proportions republished information found elsewhere (24.3%) and personal texts (23.7%) (see Figure 4). show indeed that the label "Social Networking Sites" is not particularly clear for some participants. For instance, some answered Google, Yahoo, Bing, Gmail, Mozilla or Hotmail. It is a limitation of the webbased questionnaire methodology that some respondents could misunderstand the exact subject of the survey, even though a short and as clearer as possible definition was provided. With hindsight, this is unsurprisingly: as mentioned in the introduction, SNSs is a term that is often used imprecisely in everyday situations and teenagers are likely to have approached the survey with their own pre-formed understandings of the term. A better knowledge of teenagers' understanding of SNSs is necessary and could be achieved through face-to-face interviews. Furthermore, this would allow teenagers' understanding of the concept of information itself and information seeking to be addressed. This is thus why we have considered our study to be explorative. That being said, we want to focus here explicitly on information practices with SNSs.

Around 20% of young people said they never used SNSs for information seeking and a number indicated that they felt that to do so would not be appropriate: "I don't search for information on social networking sites", "I don't use these sites to find out information, I use the BBC news app for news and google for other purposes", "None, why would I, stupid question". Here again, it's quite impossible to say whether the respondent never uses SNSs to seek information or if he or she thinks what they search for on SNSs is not really "information". However our results demonstrate that, as stated by our first research question, SNSs are, indeed, information sources for most of these teenagers. Approximately four-fifths of the respondents said they use SNSs to seek information occasionally or regularly. Although some SNSs were primarily used for general purposes, others such as Google+ were more likely to be used for information seeking.

Even SNSs with a strong social element such as Facebook were regarded as information sources by large proportions of those surveyed. These results suggest it is important to look deeper into the question of the multiple motivations for using SNSs. They demonstrate that social motivations, such as maintaining the links with friends and following conversations, are definitely not the only motivation for teenagers to make use of social networking sites. These results thus confirm the data presented into the literature review as to the informational motivation to make use of SNSs, especially among teenagers. Moreover, this research has provided specific data regarding teenagers at high school level, in contrast to older university students on whom the majority of research to date has been focused. Our findings suggest that, like their older peers, 15-19 year olds make use of a wide range of possible information sources, including those sources where social interaction plays a decisive role With regard to the second research question, our research found that the kinds of information teenagers most commonly looked for on SNS were related to social activities: information about friends and social events.

This in itself is a quite predictable result. But we also found that information about wider issues was important too as SNSs were commonly used to find out about national or international news. Our results here complement those from the JAMES study [START_REF] Willemse | JAMES -Jeunes, activités, médias: enquête Suisse[END_REF] about the information topics sought by the teenagers via SNSs. Indeed, as mentioned in our literature review, the JAMES study reports the key rank occupied by SNSs within digital information practices of young people, but JAMES gives no indication about the specific areas of life or themes covered by these information seeking uses. Our study and the categories we have identified bring to light the variety of areas covered by these informational uses of SNS, from cultural events to health. Here again face-to-face interviews might be helpful to find out more categories or also to refine those we suggested.

At this stage, one of the most interesting results is that although academic purposes for information seeking were not among the most common reasons for using SNSs for information purposes, the study indicates that many students do use SNSs for academic purposes as well as for everyday life information seeking. So, while respondents say they use SNS in order to find information related to the national and international news, culture, beauty or fashion, they also report using SNSs to find information linked to the school setting and academic tasks. Searching for information on SNS following the request of a teacher comes in sixth place (27.7%) of the 13 predefined categories in our questionnaire. It is also worth noting that, unlike information seeking for some everyday purposes, there were no significant differences between male and female students in their use of SNS for academic-related information seeking. Within our questionnaire, two other categories are related to information seeking based on academic tasks: "information for a school project on your own" (20.3%), "an extension of a lesson" (20.1%). Another category is closely linked to academic concerns: "information related to educational/vocational guidance" (22.4%). The information use of SNS for academic purposes among high school students is therefore far from insignificant despite the dismissive attitudes often in evidence, as mentioned in the introduction. In follow up interviews it would be interesting to explore whether independent use of SNSs for academic tasks is encouraged (or accepted) only by certain teachers or in particular subjects, or whether it is something that students engage in across the curriculum. It would also be valuable to consider exactly how teenagers make use of such resources for academic purposes, and whether they receive any guidance or training from teachers or librarians in doing so.

Implications for theory building

From the perspective of the « information grounds » theory, the results presented here suggest that SNSs could be considered as online "information grounds". Based on the seven propositions that define "information grounds", Scott Counts and Karen Fisher already showed in their study of SLAM, a mobile messaging device, that an online platform can be thought as an information ground [START_REF] Counts | Mobile Social Networking: an information grounds perspective[END_REF]. With SNSs, formal and informal social interaction is usually a primary purpose but information sharing can also occur. As our respondents were teenagers, the significant role of academic tasks in these processes should be noted and may be compared with the role of professional tasks for adult groups. The surveyed teenagers reported that they use SNSs to satisfy information needs. From the perspective of the ELIS model, informational uses of SNSs here are clearly associated with everyday life and ordinary socialization, but they are also related to school tasks including those which are prescribed or compulsory.

These results also let us see different uses of SNSs uses that may even appear to be seemingly contradictory (friends and socialization on one hand, educational tasks on the other hand) but which are mixed in the reality of these teenagers' practices. This is a specific illustration of the porosity of contexts which the works of Stefana [START_REF] Broadbent | Intimacy at Work: how digital media bring private life to the workplace[END_REF] highlighted. These results underpinned the necessity for the researchers to take regarding specifically these social sources. The results of this survey put a different perspective on the training objectives set by the information literacy standards especially those which promote a wider approach, not only focused on digital media, such as Transliteracy. Nowadays, the expert is indeed the one who is able to benefit from different, or even opposing, information sources or media, and to use them equally. While the results have demonstrated that SNSs are used in academic tasks, SNSs are still banned from many schools, associated with teenage life and juvenile socialization, essentially viewed from the perspective of risk and protection of personal data. These results reaffirm the necessity to take into account the important role of social interactions in the information processes that are definitely not merely a simple relationship between an individual and an information system. In line with the paradigm of Transliteracy, our results help to point out educational and social issues at stake in the different types of SNSs uses.

Conclusion

While this study has some limitations as explained above, it suggests promising areas for further research and in particular reflections about the relevance of current IL guidelines and training by highlighting the importance of teenagers' SNS usage. SNSs, in particular Facebook, YouTube, and Twitter, are used by the teenagers who responded the questionnaire to search for information. Regarding tasks directly related to education and school, SNS are used to find information for a task at the direction of a teacher but also for school projects not explicitly directed by teacher and about topics not taught in class. In addition, SNSs are used to search for information related to educational and vocational guidance. The school oriented searches are, therefore, far from being meaningless in these results and suggest it is possible to investigate school and academic tasks as a possible information ground "lever", engaging people in both formal and informal information sharing. By highlighting the role of SNSs as an information source for teenagers both within school and beyond, this research has stressed the porosity that exists between the two "opposing" settings: everyday life and school. While SNSs are frequently described as typical tools in teenagers' social lives, we should keep in mind that the same SNSs could equally be used for academic purposes. Although information grounds theory has not traditionally included school contexts, we would argue that this approach offers a potentially fruitful framework within which to explore the ways in which teenagers use SNSs, not only as communication tools, but as information sources.

This research draws attention to the importance of Transliteracy, or more specifically, taking SNSs into account alongside a wide range of information sources, from word of mouth to books, when designing IL guidelines and media awareness programmes. Research considering SNSs as information sources has the potential to enhance the knowledge about human relationships as an information source, which has been shown to be an important means for information seeking and sharing. It could also contribute to better understanding the information seeking activity in a Web 2.0 context, still for the most part overlooked (Hyldegård, 2009;Boubée and Tricot, 2010).

Figure 1 :

 1 Figure 1: How often do you use these social networking sites to seek information? (n=473)

Figure 2 :

 2 Figure 2: What kinds of information do you look for on these SNSs? (n=473)

Figure 3 :

 3 Figure 3: In general, how often are you satisfied with the quality and reliability of information you find on SNSs? (n=473)

Figure 4 :

 4 Figure 4: Do you publish information on SNSs? (n=473)

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-forprofit sectors.

into account the reality of everyday life, ordinary and tiny, information uses but also the theoretical need to re think ELIS models in the light of this interlacing of contexts, school included and not only work as ELIS model has been elaborated.

Daily information practices are crucial and particularly for young people's personal development, for example, regarding personality, citizenship and the lifelong learning skills, and these have been shown to be more heterogeneous than different [START_REF] Livingstone | Gradations in digital inclusion: children, young people and the digital divide[END_REF]Hargittai and Hinnant, 2008;[START_REF] Mercklé | La stratification sociale des pratiques numériques des adolescents[END_REF]Hatlevik and Christophersen, 2013;boyd 2014). Indeed provision or access are not sufficient on their own to create use, and practices can be very different, even discriminating, from an individual to another. As Gil de Zuniga (2009: 321) mentioned regarding information motivations and political participation: "(…) it is not the media per se that can affect individuals' social capital and engagement, but the specific ways individuals use media". Despite many critiques of the concept, the "digital natives" representation is still often used to describe the digital practices of teenagers in a global way and on a generational divide basis. But it seems essential to better understand these practices at a personal level, their evolution through the interaction with others, the multiplicity of information sources and the relations between different settings [START_REF] Octobre | Les horizons culturels des jeunes[END_REF][START_REF] Zaffran | La recomposition des pratiques culturelles des adolescent(e)s : terrain français, éclairages québécois[END_REF]. In the same way, this research could highlight the heterogeneity of young people's uses of SNSs for information purposes.

There is clearly not a single model 'digital native'; teenagers differ in their attitudes towards SNSs as information sources; the specific SNSs used; the information purposes for which they used SNSs; and their publishing habits. While some teenagers make use of a wide range of SNSs for both academic and everyday purposes, others restrict their information seeking to non-academic purposes, or do not feel they use SNSs for information seeking at all. A question for further research is whether some teenagers make limited use of SNSs for information purposes because they lack the skills needed to do so. Although they may possess the information literacy skills needed to use more traditional information resources, including online resources, effectively, they may not have the range of literacies required to seek information from SNSs. This appears a likely scenario as comments from some students indicate that they were not even open to the possibility of searching for information using SNS. Heterogeneity can be perceived also in the declared publishing uses of SNSs: only 23.7% of the respondents said that they publish personal texts on SNSs, and 16.5% declared that they never publish content of any kind there. It could be relevant to better understand the motivations of these publishing habits, as well as the academic uses of SNSs, in the light of work of [START_REF] Lampe | Student use of Facebook for organizing collaborative classroom activities[END_REF] who showed that students may use SNSs such as Facebook to perform academic tasks or homework assignments and to discuss about school life or teachers' instructions.

The significant position of SNSs in teenagers' information landscapes, demonstrated through the findings reported above, should encourage educators to consider this type of sources while designing information literacy training programs and especially while developing critical thinking strategies and curricula

Conditions


S Jiquel

B Marandat

D Berthet

F Vigouroux

F Zachos

C Argot

V Bouëtel

J Lésur

P Lister

R Brewer

We conducted DMTA [2] on shearing and grinding facets (Fig. 2) of the protocone and protoconid/hypoconid of molars first in extant rhinoceros. We built a database with 62 wild shot specimens distributed in the five living species.

Then, we used this database to infer the diet of the three fossil samples of Stephanorhinus from France (Fig. 3). All specimens (extant and fossils) are kept in various European museum collections. We chose to study the impact of these climatic changes on rhinoceros diets using dental microwear texture analyses (i.e., DMTA) because:

Discussion and Conclusions

-rhinoceroses are abundant and diverse in the fossil record [1]; -extant rhinoceroses have various herbivorous diets (Fig. 1); -DMTA is a powerful tool to study diet and infer paleodiets. White rhinoceros and its calf grazing

Results

Figure 5: Bubble charts of the percentage of anisotropic specimens against that of complex ones.

Concerning the statistics:

-MANOVA on box cox transformed data suggested differences by facet (df= 1, p-value ~10 -5 ) and species (df= 7, p-value > ~4.10 -5 ). For fossils alone, no interspecific differences (df= 2, p-value ~0.1).

-ANOVA revealed that anisotropy explains interspecific differences, FTfv facet differences and complexity both (all p-values < 0.01). In Fig. 4, the results of post-hoc tests are shown when significant.

Few fossil specimens are anisotropic ([3,4]; epsLar > 0.005): less than 20% for both facets and species, except for shearing of Stephanorhinus etruscus (Fig. 5). We focused on three French samples of distinct species of Stephanorhinus of different ages and localities (see materials).

We calculated and plotted the mean and standard deviation for three textural parameters (Fig. 4), from top to bottom: anisotropy (epsLar), complexity (Asfc) and fine textural fill volume (FTfv).

Extant species display significant differences in their microwear. The high anisotropy for the Sumatran rhinoceros was unexpected but might be due to bamboo and tough leaves consumption. Both facets provided complementary results: Grinding facet: the three Stephanorhinus samples cluster with the extant browsers D. bicornis and R. sondaicus, pointing towards similar browsing paleodiets for all three fossil samples. Shearing facet: differences between fossils and between fossil and extant samples might be due to paleodiets with no real living analog and/or to different masticatory processes.

A browsing diet for S. etruscus sample implies the persistence of local forested patches during the Pleistocene around Senèze. Yet, the greater prevalence of anisotropic specimens for this sample might reflect the incorporation of tough items in the diet such asgrasses or leaves.

Figure 3 :

 3 Figure 3: Location of the sites

Figure 1 :

 1 Figure 1: Diets of the extant rhinoceroses Dark blue: Diceros bicornis (black rhinoceros), light blue: Ceratotherium simum (white rhinoceros), brown: Dicerorhinus sumatrensis (Sumatran rhinoceros), orange: Rhinoceros unicornis (Indian rhinoceros), yellow: Rhinoceros sondaicus (Javan rhinoceros).

  1. Cerdeño, E. (1998). Diversity and evolutionary trends of the Family Rhinocerotidae (Perissodactyla). Palaecogeogr. Palaeoclimatol. Palaeoecol. 141, 13-34. 2. Scott, R.S., Ungar, P.S., Bergstrom, T.S., Brown, C.A., Grine, F.E., Teaford, M.F., and Walker, A. (2005). Dental microwear texture analysis shows within-species diet variability in fossil hominins. Nature 436, 693-695. 3. Scott, R.S., Teaford, M.F., and Ungar, P.S. (2012). Dental Microwear Texture and Anthropoid Diets. Am. J. Phys. Anthrop. 147, 551-579. 4. Merceron G., Novello, A., and Scott, R.S. (2016). Paleoenvironments inferred from phytoliths and Dental Microwear Texture Analyses of meso-herbivores. Geobios 49, 135-146.

Figure 2 :

 2 Figure 2: Precise localisation of the studied facets on second upper (left) and lower (right) molars.

Figure 4 :

 4 Figure 4: Barplots of the mean values of three textural parameters by species and by facet. Asfc: complexity; epsLar: anisotropy; FTfv: fine textural fill volume (0.2μm)

Acknowledgements


Bérenger Gans
email: berenger.gans@u-psud.fr

Gustavo A Garcia

Séverine Boyé-Péronne

Stephen T Pratt

Jean-Claude Guillemin

Alfredo Aguado

Octavio Roncero

Jean-Christophe Loison

Origin band of the first photoionizing transition of hydrogen isocyanide

The photoelectron spectrum of the X 1 Σ + → X + 2 Σ + ionizing transition of hydrogen isocyanide (HNC) is measured for the first time at a fixed photon energy (13 eV). The assignment of the spectrum is supported by wave-packet calculations simulating the photoionization transition spectrum and using ab initio calculations of the potential energy surfaces for the three lowest electronic states of the cation. The photoelectron spectrum allows the retrieval of the fundamental of the CN stretching mode of the cationic ground state ( ν3 = 2260 ± 80 cm -1 ) and the adiabatic ionization energy of hydrogen isocyanide: IE(HNC) = 12.011 ± 0.010 eV, which is far below that of HCN (IE(HCN) = 13.607 eV). In light of this latter result, the thermodynamics of the HCN + /HNC + isomers is discussed and a short summary of the values available in the literature is given.

Introduction

The [H,C,N] molecular system is one of the fundamental model systems in molecular physics, in particular for its HCN↔HNC hydrogen shift isomerization reaction. [START_REF] Mellau | [END_REF] In the interstellar medium, the hydrogen isocyanide molecule (HNC) is omnipresent [2][3][4][5][6][7][8][9] with a comparable abundance to that of the hydrogen cyanide (HCN), its more stable isomer. 10 These two molecules and their corresponding cations are involved in numerous reactions. For instance, Loison et al. 10 have listed more than 50 reactions of these species in a chemical network describing dark molecular clouds. It is thus crucial to have a good knowledge of the thermochemical data to establish the most important sources and sinks of these species. The HCN + /HNC + ratio is a puzzling matter in interstellar media. HCN + /HNC + isomers are produced through various ion-molecule reactions: H + + HCN, H + + HNC, CN + + H 2 , N + CH + 3 , CN + H + 3 . In dense molecular clouds, knowledge of the specific isomer HCN + /HNC + is not essential, because both are expected to react rapidly with H 2 leading to HCNH + + H. 10,11 For diffuse molecular clouds, however, hydrogen is primarily present as H atoms, and the main destruction pathway for HCN + /HNC + is electronic dissociative recombination, for which the rate is 30 times larger for HCN + than HNC + . 12 For the reaction with H + , the ionization energy (IE) is 13.598 eV for H 13 , 13.607 eV for HCN, 14 and around 12 eV for HNC (see Section 3.2). Then, as the rate constant for the H + + HCN reaction is very high at room temperature, 11 close to the Langevin one, the product is likely HNC + and not HCN + . The CN + + H 2 reaction has been studied by Petrie et al. 15 and Scott et al. 16 They found that it is a fast reaction producing equal amounts of HCN + and HNC + , the isomers being identified through their different reactivity with CO and CO 2 . The N + CH + 3 reaction is supposed to lead only to HCN + isomer. 17,18 There is no data for the CN + H + 3 reaction but considering the potential energy curves, both isomers should be produced because both H-CN + and H-NC + approaches are barrierless. 12,19 It is then important to introduce both isomers in astrochemical networks with relevant rates and branching ratios.

Although the enthalpies of formation of HCN [START_REF] Chase | NIST-JANAF THERMOCHEMICAL TABLES[END_REF]21 and HCN + (see Section 3.4) are well known, the values for HNC and HNC + are less certain. In particular, although a few theoretical [22][23][24][25][26] and experimental 27,28 works are available in the literature, the value of the ionization energy of HNC is still uncertain, as reflected in the range of values reported in the literature (IE calc. = [11.48 -12.01] eV and IE exp. = [12.04 -12.5] eV).

The main drawback of this lack of data is that the two iso-mers are often described as same species with the same thermodynamic properties. This crude approximation can be a source of error, particularly in reactions like H + + HCN/HNC → H + HCN + /HNC + , which are either endothermic or exothermic at low temperature (see below).

In this paper, we present the first measurement of photoionizing transitions of HNC in the vicinity of the X 1 Σ + → X + 2 Σ + transition, supported by ab initio calculations.

Methods

Experimental details

The spectrum presented in this paper has been recorded at the DESIRS beamline of the SOLEIL French synchrotron facility 29 with the DELICIOUS III spectrometer. 30 To generate the HNC molecules, we used a flow-tube reactor inducing H-abstraction from a chosen hydrogenated precursor by reaction with F atoms. (see Ref. 31 for detailed information). The F atoms are produced by a microwave discharge applied to a gas mixture of F 2 diluted in helium. The precursor, also diluted in helium, is introduced in the flow-tube with an adjustable concentration with respect to that of fluorine atom to yield multiple H-abstractions and thus to generate both HCN and HNC isomers.

In the present study, the precursor was methanimine (HN=CH 2 ) which leads to both isomers, HCN and HNC depending on which hydrogens are removed. It has been synthesized following an improved version of the procedure described in Ref. 32. A tube (30 cm) and two U-traps equipped with stopcocks were fitted on a vacuum line (0.1 mbar). The tube was half-filled with powdered potassium hydroxyde (50 g) and heated up to 90 • C. The first trap was immersed in a cold bath (-80 • C) and the second one in liquid nitrogen. Aminoacetonitrile (2.8 g, 50 mmol) was slowly vaporized on KOH. High boiling point impurities were trapped in the first trap and methanimine in the second one. At the end of the reaction, the stopcocks of the second U-trap were closed and the compound kept in liquid nitrogen (yield: 0.75 g, 52%, 26 mmol).

HN=CH 2 was introduced in the experiment using its vapour pressure at -78 • C (dry ice temperature). The flow-tube reactor conditions were optimized to favor two successive H-atom abstractions i.e. the HNC (and HCN) production. Even though the two isomers have the same mass, they have different vibronic structures, including a much lower ionization energy for the HNC isomer (IE(HNC) ≈ 12 eV, see Section 3.2), as compared to HCN (IE(HCN) = 13.607(2) eV 14 ). The ionization energy and corresponding photoelectron energies can thus be used to distinguish the two isomers with the DELICIOUS III spectrometer.

The measurement presented in this paper has been recorded at a fixed photon energy (13 eV) by averaging the signal over 9 hours. The photoelectron spectrum has been obtained from the photoelectron image by using the pBASEX algorithm 33 to extract the photoelectron kinetic-energy distribution. The ionization energies of water and oxygen, IE(H 2 O) = 101766.8(12) cm -1 (= 12.6175(2) eV) 34 and IE(O 2 ) = 97348(2) cm -1 (12.0696 eV) 35 , respectively, present in the background gas inside the spectrometer, was used to calibrate the energy scale. The resulting spectrum r γ Fig. 1 Representation of Jacobi coordinates (r, R, and γ). The H, C, and N atoms are represented in light grey, dark grey, and blue, respectively. has a spectral resolution of 60 meV at a binding energy of 12 eV (1 eV kinetic energy) 36 and the accuracy of the calibrated energy scale is about 5 meV.

Computational details

The potential energy surfaces of HCN + in the first three electronic states, two of 2 A and one of 2 A symmetry, have been calculated here. A correlation consistent F12 double zeta atomic basis set 37 , VDZ-F12, was used. Multi-configurational self-consistent field (MCSCF) calculations were performed using 8 and 2 active orbitals of a and a symmetry, respectively, optimizing the average energy of 4 states: the ground state of neutral, and for the cation, two states of 2 A symmetry and one 2 A state. With the resulting molecular orbitals, the ic-MRCI-F12 energies (internally contracted multireference configuration interaction ) of the 2 A and 2 A states of the cation were calculated using the MOLPRO suite of programs. [START_REF] Werner | MOLPRO, version 2012.1, a package of ab initio programs[END_REF] The calculations are done at geometries defined in Jacobi coordinates with r, the CN internuclear vector, R, the vector joining the CN center of mass to H, and cos γ = r • R/rR, where r and R are the modulus of the corresponding Jacobi vectors, see Figure 1. The zero energy is set at the minimum well of the X 1 Σ + ground state of HCN (at r e = 1.158 Å, R e = 1.697 Å, and γ = 180 • ), and the absolute energies of the HCN + potential energy surfaces were determined from the ab initio calculations described above.

As discussed below, the lowest electronic states of HCN + and HNC + are subject to Σ -Π vibronic couplings due to conical intersections. In order to properly describe the conical intersections, a diabatic representation is considered, formed by three states with well-defined projection of the electronic orbital angular momentum, Λ = 0, ± 1. In this 3×3 subspace, the diabatic states are coupled through the V e potential term. The Hamiltonian matrix is completely analogous to those used before for treating Σ -Π vibronic effects, 39

H e =    E -1 (r, R, γ) V 1 (r, R, γ) 0 V 1 (r, R, γ) E 0 (r, R, γ) V 1 (r, R, γ) 0 V 1 (r, R, γ) E 1 (r, R, γ)    , (1)
where

E 1 = E -1 , and V 1 (r, R, γ) ∝ sin γ, as γ → 0 • or 180 • .
The adiabatic eigenvalues of this electronic matrix are

E 1 and E ± = E 1 + E 0 ± (E 1 -E 0 ) 2 + 8V 2 1 /2
and can be associated with the ab initio points of the two 2 A and the 2 A surfaces described above. Thus the parameters E 0 , E 1 , and V 1 can be directly obtained from the ab initio calculations as previously done for the OHF system [START_REF] Gómez-Carrasco | [END_REF] .

With the three-dimensional set of ab initio points, the diabatic potential energy surfaces, E 0 and E 1 , and the coupling, V 1 , of HCN + are interpolated using 3D cubic splines, with the DB3INK/DB3VAL subroutines based on the method of de Boor 41 and distributed by GAMS. [START_REF] Boisvert | [END_REF] The photoelectron spectrum of HNC isomer is calculated using a wave-packet method similarly to that applied to calculate the photodissociation of HCN 43,44 and photodetachment of OHF -. [START_REF] Gómez-Carrasco | [END_REF] In the present approach, the transition dipole moment is neglected, and the initial wave-packet is the rovibrational wave function of the neutral HNC isomer. Here we consider three independent transitions, in which the initial wave-packet is placed on one of the 3 diabatic states of the cation. The wave-packet is then propagated within the coupled diabatic representation, using the MADWAVE3 code. 45,46 The spectra are calculated by doing a Fourier transform of the autocorrelation function. We have propagated the wave-packets for about 10 5 iterations, so that doing the Fourier transform integration within a given time window, the resulting simulated spectra are broadened by a homogeneous width of approximately 0.5 meV, much narrower than the experimental resolution (see Section 2.1).

Results and discussion

3.1 Topography of the HCN (+) /HNC (+) isomerization

The minimum energy path calculated at each angle γ (optimizing r and R for each value of γ) is presented in Fig. 2. In Table 1, the optimized values of r and R for γ = 180 • and 0 • are reported. The values obtained for the 1 [START_REF] Mellau | [END_REF] A surface are in good agreement with experimental works. 47,48 Table 1 Optimized geometries of the HCN (+) /HNC (+) neutral and cationic isomers (calculated in this work unless specified). All the values are in Å.

γ = 180 • (HCN (+) ) γ = 0 • (HNC (+) ) r e R e r e R
1 1 A' X 1 Σ + X 1 Σ + X + 2 Π A + 2 Σ + A + 2 Π X + 2 Σ + 1 2 A' 1 2 A'' 2 2 A' HCN HNC
angle γ / °e nergy / eV Fig. 2 Minimum energy path for the HCN/HNC and HCN + /HNC + isomerization in the ground state of the neutral and the lowest electronic states of the cation as a function of γ, with r and R parameters optimized for each value of γ. (See Figure 1 for geometry conventions.)

ground state of HCN + at γ = 180 • and splitting in one 2 A and one 2 A components in the C s symmetry group when the system bends. The third state is slightly higher in energy at γ = 180 • and corresponds to the first excited state ( 2 Σ + ) of HCN + . Like one of the components of the ground state, the 2 Σ + state becomes a 2 A state when 180 • > γ > 0 • . The lowest 2 A component gives rise to the X + 2 Σ + ground electronic state of HNC + and the upper one, combined with the 2 A component, lead to the 2 Π excited states of HNC + at γ = 0 • . Because they have the same symmetry, the two 2 A components stemming from the two lowest electronic states ( 2 Σ + and 2 Π states) of HCN + interact and thus repel each other. This situation is typical near a conical intersection between the two 2 A states, giving rise to important Σ -Π vibronic couplings, as reported for this system by Köppel et al. 49 The conical intersection is clearly seen in the bottom panel of Fig. 3, at a r distance slightly shorter than the equilibrium distance of the well of the neutral HCN (r e = 1.158 Å). At this linear configuration, the equilibrium r e distances of the 2 Σ and 2 Π states shift to lower and longer r e distances, respectively. The large change of the r value upon ionization towards the 2 Π state and the Σ -Π vibronic couplings lead to the vibrational progression observed in the HCN photoelectron spectrum. 14,[49][50][51][52] The situation for the HNC + isomer, at γ = 0 o , is rather different. In this case the 2 Σ(= 1 1 A ) state shifts to lower energy, resulting in a shift of the conical intersection towards considerably larger r values (top panel of Fig. 3). As a consequence, the Σ and Π states have a rather different energy and they do not strongly interact at r e = 1.166 Å, in the Frank-Condon region. In addition, the 2 Σ state for the HNC + isomer has an equilibrium distance very close to that of neutral HNC. From that, one can expect to observe a re- energy / eV duced vibrational progression in the HNC photoelectron spectrum with respect to the one of HCN.

• • • • • • • • • • • • • • • • • • • • • • • • 1.0 1.
• 1 2 A' 1 2 A'' 2 2 A' • • • • • • • • • • • • • • • • • • • • • • • • • • 1.0 1.
r / A °e nergy / • 1 2 A' 1 2 A'' 2 2 A'

Photoelectron spectrum of the HNC isomer

In Fig. 4, the experimental photoelectron spectrum of the X 1 Σ + → X + 2 Σ + ionizing transition of HNC is depicted (upper panel) and compared with our calculated spectrum (lower panel).

account for the experimental resolution and the rotational structures of the neutral and the cationic states (not considered in our calculation), the calculated spectrum displayed in the lower panel (grey line) has been convoluted with a Gaussian line shape (full width at half maximum (FWHM)= 80 meV). The resulting spectrum is also presented in the lower panel (black line). Note that the calculated spectrum has been shifted up in energy by 0.371 eV in order to have the origin band of the X 1 Σ + → X + 2 Σ + transition at the same energy as in the experimental spectrum. The adiabatic ionization energy of HNC is thus the only fitted parameter in our calculated spectrum.

The experimental spectrum consists of one main band located at 12.011 eV corresponding to the origin band of the X 1 Σ + → X + 2 Σ + transition and a weaker band at higher energy (12.29 eV) involving the v = 1 excited state of the cationic ν 3 vibrational mode (CN stretching mode, see below). The transition towards the 2 Π state of HNC + should appear at approximately the same photon energy as the one of HCN + as expected from the calculations. However, the PES of Fig. 4 has been recorded at 13 eV, below the IE of HCN (13.6 eV) to avoid a saturation of the spectrum by the HCN signal. Thus we cannot provide a measurement of the ionizing transition towards the first excited states of the HNC + cation.

The different values available in the literature concerning the vibrational wavenumbers of HNC + for the ν 1 (NH stretch), ν 2 (HNC bend), and ν 3 (CN stretch) modes, are compared with our results in Table 2. The overall agreement is satisfactory. From our calculations, one should expect to observe in the photoelectron spectrum transitions involving all the vibrational modes of the cation (ν 1 , ν 2 , and ν 3 ), see lower panel of Fig. 4. The calculated positions of the 2 2 0 , 3 1 0 , and 1 1 0 bands with respect to the origin band are 0.15 eV (1210 cm -1 ), 0.28 eV (2260 cm -1 ), and 0.43 eV (3470 cm -1 ), respectively, see Table 2. Nevertheless in the present work, the signal-to-noise ratio does not allow an unambiguous assignment of structures corresponding to ν 1 -and ν 2 -active transitions. Only the fundamental of the ν 3 vibrational mode can be extracted from our spectrum: ν3 = 2260(80) cm -1 (= 0.28(1) eV). This value is in very good agreement with our calculations (0.28 eV), see Table 2.

In Table 3, the IE value of HNC obtained in this work is compared with previous experimental works. For completeness, the two most accurate values for HCN are also reported. The only experimental values for HNC found in the literature are the one deduced by Hansel et al. from the HNC + + Xe charge transfer reaction 28 and the recombination energy of HNC + measured by Bieri and Jonsson. 27 Although the uncertainties do not overlap, the agreement is satisfactory.

On the side of the theory, several values have been obtained using different approaches. [22][23][24][25] The value of Koch et al. calculated using the Moller-Plesset perturbation theory (12.01 eV) presents the best agreement with our measurements. 24 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 a) Exp.

0 0 3 0 1 3 0 2 2 0 2 1 0 1 X 1 Σ + → X + 2 Σ + X 1 Σ + → A + 2 Π
energy / eV Fig. 4 Photoelectron spectra of HNC: experimental spectrum recorded at 13 eV (upper panel) and calculated spectrum between 11 and 15 eV (lower panel). In the lower panel, the grey line is the calculated spectrum and the black line its convolution with a gaussian line shape (FWHM = 80 meV). a Deduced from the HNC + + Xe charge transfer reaction.

b Estimation, value of the recombination energy of HNC + .

Photoelectron angular distribution of HNC

The normalized photoelectron angular distribution is described by the parameter, β , through the expression:

I(θ ) = 1 + β /2 × (3cos 2 (θ ) -1) (2)
where θ is the polar angle of ejection with respect to the ε polarization vector of the light (see Fig. 5). The β values have been extracted from the photoelectron image shown in Figure 5 for the transitions to the v = 0 (origin band) and v 3 = 1 (v 3 = 1 band) levels of cationic ground state, and correspond to 1.14 and 1.2, respectively. In the absence of theoretical calculations of the photoionization process, which are not within the scope of the present article, we can only compare these values to those found in HCN. In HNC, the highest occupied molecular orbital (HOMO) corresponds to the 5σ orbital, and the (HOMO-1) corresponds to the 1π orbital, while in HCN, the ordering of these two orbitals is reversed. Holland et al. 56 have reported the β parameters for ionization from these two orbitals close to threshold. For the 1π orbital, the origin and v 3 = 1 bands gave β values around 0.0 and 0.25, respectively. Unfortunately, the photoelectron bands for ionization from the 5σ orbital were overlapped by signal from ionization to higher vibrational levels from the 1π band. Nevertheless, the β value extracted for these overlapped bands near threshold is ≈ 0.4, somewhat higher than for ionization from the 1π orbital of HCN. This observation is consistent with the present one for HNC, where ionization from the 5σ orbital is more anisotropic and gives a relatively large value of β .

Thermodynamics of the HCN/HNC isomers

The enthalpy of formation of HCN is well known and the preferred value in the literature is 135.1(84) kJ.mol -1 . [START_REF] Chase | NIST-JANAF THERMOCHEMICAL TABLES[END_REF]21 Using the precise value of the ionization energy of HCN reported by Fridh and Åsbrink, 14 one can deduce the enthalpy of formation of HCN + (∆ f H • (HCN + ) = 1448.0(84) kJ.mol -1 ). These two values are compatible with the ones of the Active Thermochemical Tables, [START_REF] Ruscic | Active Thermochemical Tables (ATcT) values based on ver. 1.122d of the Thermochemical Network[END_REF][START_REF] Nguyen | [END_REF] see Table 4.

Although the enthalpy of formation and the IE of HCN are well known, there is relatively little direct experimental data for HNC. Hansel et al. measured the endothermicity of the HNC + + CO → HCO + + CN reaction (31 kJ.mol -1 ). 28 From this value, they derived the enthalpy of formation of HNC + , using literature data. In their paper, the source of the data from the literature was not unambiguously given. Thus, we propose here to use other values from the literature combined with their result. Using ∆ f H(CO) = -110.5 (10) kJ.mol -1 , 21 ∆ f H(HCO + ) = ∆ f H(HCO) + IE(HCO) = 42(1)+ 786.377(6) kJ.mol -1 , 59,60 and ∆ f H(CN) (434.5 (20) kJ.mol -1 61 or 439.7(48) kJ.mol -1 62,63 ), we obtain ∆ f H(HNC + ) = 1342(3) kJ.mol -1 or 1348(3) kJ.mol -1 . Note that Hansel et al. obtained 1349(4) kJ.mol -1 close to the latter value.

Using our IE(HNC) = 12.01(1) eV and the two values of ∆ f H(HNC + ) derived above, we obtain ∆ f H(HNC) = 184(3) kJ.mol -1 or 189(3) kJ.mol -1 , respectively. The latter value is in good agreement with the one from the Active Thermochemical Tables with respect to the error bars, [START_REF] Ruscic | Active Thermochemical Tables (ATcT) values based on ver. 1.122d of the Thermochemical Network[END_REF] see Table 4.

In addition, there are two direct measurements of the energy difference between HNC and HCN. First, Maki et al. performed a HCN/HNC equilibrium measurement at high temperature using spectroscopic HNC absorption. [START_REF] Maki | [END_REF] Their measurement gave an energy difference (∆E neutral iso. ) between HNC and HCN of 3600(400) cm -1 = 43.1(48) kJ.mol -1 . Using this value and the enthalpy of formation of HCN, one can deduce the enthalpy of formation of HNC (∆ f H 0 = 178(10) kJ.mol -1 ). One year later, Pau and Hehre measured the energy difference between HNC and HCN (∆E neutral iso. = 61.9(83) kJ.mol -1 ) using pulsed ion cyclotron double resonance spectroscopy 65 which leads to an enthalpy of formation of HNC of 197( 12) kJ.mol -1 . It is difficult to explain the differences between the value of Maki et al. and the one of Pau and Hehre, but the results obtained by Pau and Hehre are suported by theoretical calculations (∆E neutral iso. = 59.4 kJ.mol -1 ). 66 In addition, one could argue that at high temperature HCN and HNC have a non-negligible reactivity that may affect the HCN/HNC equilibrium; thus, the measurement of Maki et al. may be biased. Using the enthalpies of formation of HCN and HNC from the the Active Thermochemical Tables, [START_REF] Ruscic | Active Thermochemical Tables (ATcT) values based on ver. 1.122d of the Thermochemical Network[END_REF] we obtain ∆E neutral iso. = 63.117 kJ.mol -1 , which is in better agreement with the value of Pau and Hehre.

From the discussion above, the values proposed by the Active Thermochemical Tables, [START_REF] Ruscic | Active Thermochemical Tables (ATcT) values based on ver. 1.122d of the Thermochemical Network[END_REF] seem to be very accurate and always confirmed by experimental measurement. Note that from the enthalpy of formation of HNC and HNC + proposed by these tables, one can derive an IE value for HNC of 12.028 (14) eV, in very good agreement with our present measurement (12.01(1) eV).

Concluding remarks

Using a flow-tube reactor and a suitable precursor (HN=CH 2 ), the hydrogen isocyanide isomer (HNC) has been efficiently produced in the gas phase, and its photoionization has been studied for the first time at a fixed photon energy (13 eV). The recorded photoelectron spectrum is in good agreement with the photoionizing transition spectrum predicted by wave-packet method based on ic-MRCI ab initio calculation of the potential energy surfaces for the HCN/HNC system. The differences in the photoelectron spectra of the HCN and HNC isomers are explained by the different energy landscapes of their respective Franck-Condon regions. For HCN, a conical intersection between two of the three lowest potential energy surfaces of the cation occurs close to the equilibrium geometry of the HCN ground state, giving rise to important vibronic couplings in the ground state of the cation. This affects the vibrational progressions in the HCN photoelectron spectrum in the vicinity of the first ionization energy. 14,[49][50][51][52] On the contrary, for HNC no such vibrational progression is expected since the conical intersection is located far from the HNC equilibrium geometry and at higher energy. The experimental spectrum, recorded for the X 1 Σ + → X + 2 Σ + transition, exhibits mainly the 0 0 0 origin band and a vibrational band corresponding excitation of the cationic CN stretching mode (ν 3 ), for which the fundamental is measured at ν3 = 2260(80) cm -1 .

The calculations of the present work predict another photoionization transition, X 1 Σ + → A + 2 Π, involving the first excited electronic state of HNC + and resulting in an extended vibrational progression between 13.7 and 15 eV. It would be very interesting to design a gas-phase source enable to produce efficiently the HNC isomer only. This would allow to confirm our prediction and to investigate the vibronic structure of the first excited electronic state of the cation.

The β anisotropy parameter for the origin band and the v 3 = 1 band is extracted from the photoelectron angular distribution of HNC with values around 1.14 and 1.2 larger than what was measured for HCN. This finding is consistent with the different HOMO involved in the photoionization process.

Finally, the measurement of the first adiabatic ionization energy of HNC (IE(HNC) = 12.01(1) eV) can be used in combination with the formation enthalpy of HNC + found in the literature to derive the formation enthalpy of neutral HNC: ∆ f H(HNC) = 184(3) kJ.mol -1 or 189(3) kJ.mol -1 , depending on which value of the literature is employed for the enthalpy of formation of CN. It appears that the calculated thermodynamic data available in the Active Thermochemical Tables 57 are all in agreement with the experimental values for the HCN (+) /HNC (+) isomers. Their very small error bars make them the preferred values for the thermodynamics of these species.

  Fig.2exhibit two minima at collinear geometries (γ = 180 • and 0 • ), corresponding to the HCN (+) and HNC (+) isomers, respectively.For HCN + , three states are very close in energy at linear configuration. Two of them are degenerate, forming the 2 Π electronic

Fig. 3

 3 Fig. 3 Potential energy curves of the three lowest electronic states of HCN + /HNC + system for R = 1.697 Å and γ = 180 • (HCN + isomer, bottom panel), and for R = 1.531 Å and γ = 0 • (HNC + isomer, top panel). The degeneracy of the blue lines (full or dashed) and the red circles corresponds to the 2 Π state. The vertical dotted lines indicate the r e equilibrium distances of the neutral HNC (r e = 1.166 Å) and HCN (r e = 1.158 Å) isomers.

  intensity 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 b) Calc.

  0

Fig. 5

 5 Fig. 5 Photoelectron image of HNC recorded at 13 eV photon energy. The left side shows the raw image, while the right side shows the outof the pBasex algorithm. The positive anisotropy discussed in the text is clear for the transitions to both the origin and the v 3 = 1 levels of the cation. The white arrow indicates the polarization vector of the synchrotron radiation.

Table 2

 2 Vibrational wavenumbers of the HNC + electronic ground state.

	Mode	Wavenumber / cm -1	Method	Ref.
	ν 1	3470	calc.	this work
		3404	calc.	26
		3464	calc.	25
		3365.0	exp. a	53
	ν 2	605	calc.	this work
		523	calc.	26
		618	calc.	25
		577.7 or 584.5 b	exp. a	53
	ν 3	2260	calc.	this work
		2163	calc.	26
		2212	calc.	25
		2260	exp.	this work c
		2195.2	exp. a	53

a Measured in neon matrix. b Observed but not assigned to ν 2 by the authors. The NIST recommends 577.7 cm -1 . 54 c ±80 cm -1 .

Table 3

 3 Experimental values of the first ionization energy of the hydrogen cyanide isomers.

		IE /eV	Ref.
	HNC	12.011(10)	this work
		12.04(1) a	28
		12.5(1) b	27
	HCN	13.607(2)	14
		13.606(3)	55

Table 4

 4 Enthalpies of formation of the hydrogen cyanide isomers, their cations, and the CN radical at 300 K.∆ f H • / kJ.mol-1

	Ref.

| 1-8

| 1-8

Acknowledgements

This work was performed on the DESIRS beamline under Proposal No. 20160376. We acknowledge SOLEIL for provision of synchrotron radiation facilities and the DESIRS beamline team for their assistance. This work received financial support from the French Agence Nationale de la Recherche (ANR) under Grant No.


Aakar Gupta

Thomas Pietrzak
email: thomas.pietrzak@univ-lille1.fr

A New Haptic Interaction Paradigm

Keywords: Haptics, Tactile, Interaction, ACM Classification H.5.2 [Information interfaces and presentation]: User Interfaces -Haptic I/O

Existing tactile experiences are limited to providing feedback or conveying pattern information to the user. In this position paper, we discuss how mid-air haptics are uniquely suited to explore wholly independent haptic interaction paradigms which allow the user to interact with a computer completely using her tactile and kinesthetic sense without the presence of a visual interface.

Introduction

Current haptic technologies have enabled advanced user experiences. However, these experiences almost always function as haptic patterns to convey infomrmation to the user or as assistive feedback to a visual interface.Engaging with visual displays is not always feasible or desired. At this stage of haptics, an exploration is needed into the possibilities of a wholly independent haptic interaction paradigm which allows the user to interact with a computer completely using her tactile and kinesthetic sense without the presence of a visual interface. While one could argue that such independent interactions exist in bits and pieces, an interaction paradigm akin to direct manipulation in visual displays is missing in haptic displays. Owing to its unique affordances, mid-air ultrasound haptics could be uniquely suited to explore such interaction paradigms.

Exploration into a Haptic Interaction Paradigm

The concept of direct manipulaton underlies almost all of the visual interfaces we use today. These could be indirect pointing interfaces that utilize a pointer to manipulate objects, or direct pointing interfaces that allow the user to manipulate these objects directly via touch or other means. A notion analogous to direct manipulation is absent in haptic displays. One of our upcoming papers in CHI 2016 [START_REF] Gupta | Direct Manipulation in Tactile Displays[END_REF] raises this issue and introduces the concept of direct manipulation for tactile displays that are instrumented on the skin. We describe how concepts analogous to a visual display can be adapted into a tactile context, such as a tactile screen, tactile pixel, tactile pointer, and tactile targets. However, there are a lot of open questions.

There are multiple facets to such interaction paradigms that need exploration: tactile vs haptic displays, 1D vs 2D vs 3D displays, direct pointing vs indirect pointing vs something completely novel, and different body and skin regions and their unique constraints. Looking at its demonstrated capabilities, mid-air haptics can potentially address a lot of these questions. It actuates multi-point mid-air haptic sensations with users being able to distinguish different properties of points at small separations [START_REF] Carter | Ultra-Haptics: Multi-point Mid-air Haptic Feedback for Touch Surfaces[END_REF]. Such multiplicity of points will be useful when defining a haptic interface model. Further, perception studies have shown high resolution localization and apparent motion capabilities [START_REF] Wilson | Perception of Ultrasonic Haptic Feedback on the Hand: Localisation and Apparent Motion[END_REF]. Plus, continuous 3D and volumetric haptic shapes have been rendered in mid-air using ultrasound [START_REF] Long | Rendering Volumetric Haptic Shapes in Mid-air Using Ultrasound[END_REF]. All these works plus interaction works that have demonstrated ultrasonic widgets [START_REF] Vo | Touching the invisible: Localizing ultrasonic haptic cues[END_REF] and mid-air haptic interaction with floating screens [START_REF] Monnai | HaptoMime: Mid-air Haptic Interaction with a Floating Virtual Screen[END_REF] all encourage us to think that an end-to-end haptic interaction paradigm would not only be feasible, but easily implentable and usable too with the use of mid-air haptics.