The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds
Identifieur interne : 000E14 ( Istex/Corpus ); précédent : 000E13; suivant : 000E15The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds
Auteurs : E. Sarrasin ; D. Ben Abdallah ; M. Wernli ; A. Faure ; J. Cernicharo ; F. LiqueSource :
- Monthly Notices of the Royal Astronomical Society [ 0035-8711 ] ; 2010-05-01.
Abstract
Modelling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated ab initio calculations. Calculations of pure rotational (de)excitation cross-sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross-sections for transitions among the eight first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm−1. These cross-sections were used to determine collisional rate constants for temperatures ranging from 5 to 100 K. A propensity for even Δj transitions is observed in the case of HCN–He collisions whereas a propensity for odd Δj transitions is observed in the case of HNC–He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular, in cold dark clouds for which the new HNC rates show that the j= 1 − 0 line of this species will be more easily excited by collisions than HCN. An important result of the new HNC–He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from >1 to ≃1, in good agreement with detailed chemical models available in the literature.
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DOI: 10.1111/j.1365-2966.2010.16312.x
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Faure</name><affiliation><mods:affiliation>Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS UMR 5571, BP 53, 38041 Grenoble Cedex 09, France</mods:affiliation></affiliation></author><author><name sortKey="Cernicharo, J" sort="Cernicharo, J" uniqKey="Cernicharo J" first="J." last="Cernicharo">J. Cernicharo</name><affiliation><mods:affiliation>Department of Astrophysics, CAB, INTA–CSIC, Crta Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain</mods:affiliation></affiliation></author><author><name sortKey="Lique, F" sort="Lique, F" uniqKey="Lique F" first="F." last="Lique">F. Lique</name><affiliation><mods:affiliation>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</mods:affiliation></affiliation><affiliation><mods:affiliation>LERMA and UMR 8112 of CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France</mods:affiliation></affiliation><affiliation><mods:affiliation>E-mail: francois.lique@univ-lehavre.fr</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Monthly Notices of the Royal Astronomical Society</title><title level="j" type="abbrev">Monthly Notices of the Royal Astronomical Society</title><idno type="ISSN">0035-8711</idno><idno type="eISSN">1365-2966</idno><imprint><publisher>Blackwell Publishing Ltd</publisher><pubPlace>Oxford, UK</pubPlace><date type="published" when="2010-05-01">2010-05-01</date><biblScope unit="volume">404</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="518">518</biblScope><biblScope unit="page" to="526">526</biblScope></imprint><idno type="ISSN">0035-8711</idno></series><idno type="istex">EC564E9E9324021BDFAD25EFEFB8096F7E45A716</idno><idno type="DOI">10.1111/j.1365-2966.2010.16312.x</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0035-8711</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract">Modelling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated ab initio calculations. Calculations of pure rotational (de)excitation cross-sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross-sections for transitions among the eight first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm−1. These cross-sections were used to determine collisional rate constants for temperatures ranging from 5 to 100 K. A propensity for even Δj transitions is observed in the case of HCN–He collisions whereas a propensity for odd Δj transitions is observed in the case of HNC–He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular, in cold dark clouds for which the new HNC rates show that the j= 1 − 0 line of this species will be more easily excited by collisions than HCN. An important result of the new HNC–He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from >1 to ≃1, in good agreement with detailed chemical models available in the literature.</div></front></TEI><istex><corpusName>oup</corpusName><author><json:item><name>E. Sarrasin</name><affiliations><json:string>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</json:string></affiliations></json:item><json:item><name>D. 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Lique</name><affiliations><json:string>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</json:string><json:string>LERMA and UMR 8112 of CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France</json:string><json:string>E-mail: francois.lique@univ-lehavre.fr</json:string></affiliations></json:item></author><subject><json:item><lang><json:string>eng</json:string></lang><value>Papers</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>molecular data</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>molecular processes</value></json:item><json:item><lang><json:string>eng</json:string></lang><value>scattering</value></json:item></subject><language><json:string>eng</json:string></language><originalGenre><json:string>research-article</json:string></originalGenre><abstract>Modelling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated ab initio calculations. Calculations of pure rotational (de)excitation cross-sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross-sections for transitions among the eight first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm−1. These cross-sections were used to determine collisional rate constants for temperatures ranging from 5 to 100 K. A propensity for even Δj transitions is observed in the case of HCN–He collisions whereas a propensity for odd Δj transitions is observed in the case of HNC–He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular, in cold dark clouds for which the new HNC rates show that the j= 1 − 0 line of this species will be more easily excited by collisions than HCN. An important result of the new HNC–He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from >1 to ≃1, in good agreement with detailed chemical models available in the literature.</abstract><qualityIndicators><score>8.5</score><pdfVersion>1.4</pdfVersion><pdfPageSize>595.274 x 782.286 pts</pdfPageSize><refBibsNative>false</refBibsNative><keywordCount>4</keywordCount><abstractCharCount>1685</abstractCharCount><pdfWordCount>6956</pdfWordCount><pdfCharCount>36483</pdfCharCount><pdfPageCount>9</pdfPageCount><abstractWordCount>263</abstractWordCount></qualityIndicators><title>The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds</title><genre><json:string>research-article</json:string></genre><host><volume>404</volume><publisherId><json:string>mnras</json:string></publisherId><pages><last>526</last><first>518</first></pages><issn><json:string>0035-8711</json:string></issn><issue>1</issue><genre><json:string>journal</json:string></genre><language><json:string>unknown</json:string></language><eissn><json:string>1365-2966</json:string></eissn><title>Monthly Notices of the Royal Astronomical Society</title></host><categories><wos><json:string>ASTRONOMY & ASTROPHYSICS</json:string></wos></categories><publicationDate>2010</publicationDate><copyrightDate>2010</copyrightDate><doi><json:string>10.1111/j.1365-2966.2010.16312.x</json:string></doi><id>EC564E9E9324021BDFAD25EFEFB8096F7E45A716</id><score>0.18590644</score><fulltext><json:item><original>true</original><mimetype>application/pdf</mimetype><extension>pdf</extension><uri>https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/fulltext/pdf</uri></json:item><json:item><original>false</original><mimetype>application/zip</mimetype><extension>zip</extension><uri>https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a">The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds</title><respStmt><resp>Références bibliographiques récupérées via GROBID</resp><name resp="ISTEX-API">ISTEX-API (INIST-CNRS)</name></respStmt></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>Blackwell Publishing Ltd</publisher><pubPlace>Oxford, UK</pubPlace><availability><p>© 2010 The Authors. Journal compilation © 2010 RAS</p></availability><date>2010-04-21</date></publicationStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds</title><author xml:id="author-1"><persName><forename type="first">E.</forename><surname>Sarrasin</surname></persName><affiliation>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</affiliation></author><author xml:id="author-2"><persName><forename type="first">D. Ben</forename><surname>Abdallah</surname></persName><affiliation>Laboratoire de Spectroscopie atomique, Moléculaire et applications, Faculté des Sciences Université Tunis el Manar, Tunis 1060, Tunisie</affiliation></author><author xml:id="author-3"><persName><forename type="first">M.</forename><surname>Wernli</surname></persName><affiliation>Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS UMR 5571, BP 53, 38041 Grenoble Cedex 09, France</affiliation></author><author xml:id="author-4"><persName><forename type="first">A.</forename><surname>Faure</surname></persName><affiliation>Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS UMR 5571, BP 53, 38041 Grenoble Cedex 09, France</affiliation></author><author xml:id="author-5"><persName><forename type="first">J.</forename><surname>Cernicharo</surname></persName><affiliation>Department of Astrophysics, CAB, INTA–CSIC, Crta Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain</affiliation></author><author xml:id="author-6"><persName><forename type="first">F.</forename><surname>Lique</surname></persName><email>francois.lique@univ-lehavre.fr</email><affiliation>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</affiliation><affiliation>LERMA and UMR 8112 of CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France</affiliation></author></analytic><monogr><title level="j">Monthly Notices of the Royal Astronomical Society</title><title level="j" type="abbrev">Monthly Notices of the Royal Astronomical Society</title><idno type="pISSN">0035-8711</idno><idno type="eISSN">1365-2966</idno><imprint><publisher>Blackwell Publishing Ltd</publisher><pubPlace>Oxford, UK</pubPlace><date type="published" when="2010-05-01"></date><biblScope unit="volume">404</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="518">518</biblScope><biblScope unit="page" to="526">526</biblScope></imprint></monogr><idno type="istex">EC564E9E9324021BDFAD25EFEFB8096F7E45A716</idno><idno type="DOI">10.1111/j.1365-2966.2010.16312.x</idno></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2010-04-21</date></creation><langUsage><language ident="en">en</language></langUsage><abstract><p>Modelling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated ab initio calculations. Calculations of pure rotational (de)excitation cross-sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross-sections for transitions among the eight first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm−1. These cross-sections were used to determine collisional rate constants for temperatures ranging from 5 to 100 K. A propensity for even Δj transitions is observed in the case of HCN–He collisions whereas a propensity for odd Δj transitions is observed in the case of HNC–He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular, in cold dark clouds for which the new HNC rates show that the j= 1 − 0 line of this species will be more easily excited by collisions than HCN. An important result of the new HNC–He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from >1 to ≃1, in good agreement with detailed chemical models available in the literature.</p></abstract><textClass><keywords scheme="keyword"><list><item><term>Papers</term></item></list></keywords></textClass><textClass><keywords scheme="keyword"><list><head>keywords</head><item><term>molecular data</term></item><item><term>molecular processes</term></item><item><term>scattering</term></item></list></keywords></textClass></profileDesc><revisionDesc><change when="2010-04-21">Created</change><change when="2010-05-01">Published</change><change xml:id="refBibs-istex" who="#ISTEX-API" when="2016-10-14">References added</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><original>false</original><mimetype>text/plain</mimetype><extension>txt</extension><uri>https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="corpus oup" wicri:toSee="no header"><istex:xmlDeclaration>version="1.0" encoding="utf-8"</istex:xmlDeclaration><istex:docType PUBLIC="-//NLM//DTD Journal Publishing DTD v2.3 20070202//EN" URI="journalpublishing.dtd" name="istex:docType"></istex:docType><istex:document><article article-type="research-article"><front><journal-meta><journal-id journal-id-type="hwp">mnras</journal-id><journal-id journal-id-type="publisher-id">mnras</journal-id><journal-title>Monthly Notices of the Royal Astronomical Society</journal-title><abbrev-journal-title>Monthly Notices of the Royal Astronomical Society</abbrev-journal-title><issn pub-type="ppub">0035-8711</issn><issn pub-type="epub">1365-2966</issn><publisher><publisher-name>Blackwell Publishing Ltd</publisher-name><publisher-loc>Oxford, UK</publisher-loc></publisher></journal-meta><article-meta><article-id pub-id-type="doi">10.1111/j.1365-2966.2010.16312.x</article-id><article-categories><subj-group><subject>Papers</subject></subj-group></article-categories><title-group><article-title>The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Sarrasin</surname><given-names>E.</given-names></name><xref ref-type="aff" rid="a1">1</xref></contrib><contrib contrib-type="author"><name><surname>Abdallah</surname><given-names>D. Ben</given-names></name><xref ref-type="aff" rid="a2">2</xref></contrib><contrib contrib-type="author"><name><surname>Wernli</surname><given-names>M.</given-names></name><xref ref-type="aff" rid="a3">3</xref></contrib><contrib contrib-type="author"><name><surname>Faure</surname><given-names>A.</given-names></name><xref ref-type="aff" rid="a3">3</xref></contrib><contrib contrib-type="author"><name><surname>Cernicharo</surname><given-names>J.</given-names></name><xref ref-type="aff" rid="a4">4</xref></contrib><contrib contrib-type="author"><name><surname>Lique</surname><given-names>F.</given-names></name><xref ref-type="aff" rid="a1">1</xref><xref ref-type="aff" rid="a5">5</xref><xref ref-type="corresp" rid="c1">*</xref></contrib></contrib-group><aff id="a1"><label>1</label>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</aff><aff id="a2"><label>2</label>Laboratoire de Spectroscopie atomique, Moléculaire et applications, Faculté des Sciences Université Tunis el Manar, Tunis 1060, Tunisie</aff><aff id="a3"><label>3</label>Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS UMR 5571, BP 53, 38041 Grenoble Cedex 09, France</aff><aff id="a4"><label>4</label>Department of Astrophysics, CAB, INTA–CSIC, Crta Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain</aff><aff id="a5"><label>5</label>LERMA and UMR 8112 of CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France</aff><author-notes><corresp id="c1">*E-mail: <email>francois.lique@univ-lehavre.fr</email></corresp></author-notes><pub-date pub-type="ppub"><day>01</day><month>05</month><year>2010</year></pub-date><pub-date pub-type="epub"><day>21</day><month>04</month><year>2010</year></pub-date><volume>404</volume><issue>1</issue><fpage>518</fpage><lpage>526</lpage><history><date date-type="received"><day>5</day><month>1</month><year>2010</year></date><date date-type="accepted"><day>7</day><month>1</month><year>2010</year></date></history><copyright-statement>© 2010 The Authors. Journal compilation © 2010 RAS</copyright-statement><copyright-year>2010</copyright-year><abstract><p>Modelling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated <italic>ab initio</italic> calculations. Calculations of pure rotational (de)excitation cross-sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross-sections for transitions among the eight first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm<sup>−1</sup>. These cross-sections were used to determine collisional rate constants for temperatures ranging from 5 to 100 K. A propensity for even Δ<italic>j</italic> transitions is observed in the case of HCN–He collisions whereas a propensity for odd Δ<italic>j</italic> transitions is observed in the case of HNC–He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular, in cold dark clouds for which the new HNC rates show that the <italic>j</italic>= 1 − 0 line of this species will be more easily excited by collisions than HCN. An important result of the new HNC–He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from >1 to ≃1, in good agreement with detailed chemical models available in the literature.</p></abstract><kwd-group><kwd>molecular data</kwd><kwd>molecular processes</kwd><kwd>scattering</kwd></kwd-group></article-meta></front></article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds</title></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>The rotational excitation of HCN and HNC by He: new insights on the HCN/HNC abundance ratio in molecular clouds</title></titleInfo><name type="personal"><namePart type="given">E.</namePart><namePart type="family">Sarrasin</namePart><affiliation>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">D. Ben</namePart><namePart type="family">Abdallah</namePart><affiliation>Laboratoire de Spectroscopie atomique, Moléculaire et applications, Faculté des Sciences Université Tunis el Manar, Tunis 1060, Tunisie</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">M.</namePart><namePart type="family">Wernli</namePart><affiliation>Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS UMR 5571, BP 53, 38041 Grenoble Cedex 09, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">A.</namePart><namePart type="family">Faure</namePart><affiliation>Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, CNRS UMR 5571, BP 53, 38041 Grenoble Cedex 09, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">J.</namePart><namePart type="family">Cernicharo</namePart><affiliation>Department of Astrophysics, CAB, INTA–CSIC, Crta Torrejón a Ajalvir km 4, 28850 Torrejón de Ardoz, Spain</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">F.</namePart><namePart type="family">Lique</namePart><affiliation>LOMC – FRE 3102, CNRS – Université du Havre, 25 rue Philippe Lebon, BP 540, 76058 Le Havre, France</affiliation><affiliation>LERMA and UMR 8112 of CNRS, Observatoire de Paris-Meudon, 92195 Meudon Cedex, France</affiliation><affiliation>E-mail: francois.lique@univ-lehavre.fr</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="research-article"></genre><subject><topic>Papers</topic></subject><originInfo><publisher>Blackwell Publishing Ltd</publisher><place><placeTerm type="text">Oxford, UK</placeTerm></place><dateIssued encoding="w3cdtf">2010-05-01</dateIssued><dateCreated encoding="w3cdtf">2010-04-21</dateCreated><copyrightDate encoding="w3cdtf">2010</copyrightDate></originInfo><language><languageTerm type="code" authority="iso639-2b">eng</languageTerm><languageTerm type="code" authority="rfc3066">en</languageTerm></language><physicalDescription><internetMediaType>text/html</internetMediaType></physicalDescription><abstract>Modelling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated ab initio calculations. Calculations of pure rotational (de)excitation cross-sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross-sections for transitions among the eight first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm−1. These cross-sections were used to determine collisional rate constants for temperatures ranging from 5 to 100 K. A propensity for even Δj transitions is observed in the case of HCN–He collisions whereas a propensity for odd Δj transitions is observed in the case of HNC–He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular, in cold dark clouds for which the new HNC rates show that the j= 1 − 0 line of this species will be more easily excited by collisions than HCN. An important result of the new HNC–He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from >1 to ≃1, in good agreement with detailed chemical models available in the literature.</abstract><subject><genre>keywords</genre><topic>molecular data</topic><topic>molecular processes</topic><topic>scattering</topic></subject><relatedItem type="host"><titleInfo><title>Monthly Notices of the Royal Astronomical Society</title></titleInfo><titleInfo type="abbreviated"><title>Monthly Notices of the Royal Astronomical Society</title></titleInfo><genre type="journal">journal</genre><identifier type="ISSN">0035-8711</identifier><identifier type="eISSN">1365-2966</identifier><identifier type="PublisherID">mnras</identifier><identifier type="PublisherID-hwp">mnras</identifier><part><date>2010</date><detail type="volume"><caption>vol.</caption><number>404</number></detail><detail type="issue"><caption>no.</caption><number>1</number></detail><extent unit="pages"><start>518</start><end>526</end></extent></part></relatedItem><identifier type="istex">EC564E9E9324021BDFAD25EFEFB8096F7E45A716</identifier><identifier type="DOI">10.1111/j.1365-2966.2010.16312.x</identifier><accessCondition type="use and reproduction" contentType="copyright">© 2010 The Authors. Journal compilation © 2010 RAS</accessCondition><recordInfo><recordContentSource>OUP</recordContentSource></recordInfo></mods></metadata><annexes><json:item><original>true</original><mimetype>image/jpeg</mimetype><extension>jpeg</extension><uri>https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/annexes/jpeg</uri></json:item><json:item><original>true</original><mimetype>image/gif</mimetype><extension>gif</extension><uri>https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/annexes/gif</uri></json:item></annexes><enrichments><istex:catWosTEI uri="https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/enrichments/catWos"><teiHeader><profileDesc><textClass><classCode scheme="WOS">ASTRONOMY & ASTROPHYSICS</classCode></textClass></profileDesc></teiHeader></istex:catWosTEI><json:item><type>refBibs</type><uri>https://api.istex.fr/document/EC564E9E9324021BDFAD25EFEFB8096F7E45A716/enrichments/refBibs</uri></json:item></enrichments><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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