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The investigated species include the singlet (S) and triplet (T) open\u2010chain H\uf8ffN\uf8ffC\uf8ffN<\/jats:italic><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>ions <jats:bold>1S<\/jats:bold>, <jats:bold>1S\u2032<\/jats:bold>, and <jats:bold>1T<\/jats:bold>, the open\u2010chain H\uf8ffC\uf8ffN\uf8ffN<\/jats:italic><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>ions <jats:bold>2S<\/jats:bold>, <jats:bold>2S\u2032<\/jats:bold>, and <jats:bold>2T<\/jats:bold>, the HC\uf8ffN<\/jats:italic><jats:sub><jats:italic>2<\/jats:italic><\/jats:sub><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>cyclic structures <jats:bold>3S<\/jats:bold> and <jats:bold>3T<\/jats:bold>, and the HN\uf8ffCN<\/jats:italic><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>cyclic structures <jats:bold>4S<\/jats:bold> and <jats:bold>4T<\/jats:bold>. All these species have been identified as true energy minima on the CASSCF(8,7)\/6\u201031G(d) potential energy surface, and their optimised geometries, refined at the CASSCF(8,8)\/6\u201031G(d) level of theory, have been used to perform single point calculations at the [MR\u2010CI\u2010SD(Q)]\/6\u2010311G(d,p) computational level. The most stable structure was the H\uf8ffN\uf8ffC\uf8ffN<\/jats:italic><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>ion <jats:bold>1T<\/jats:bold>, whose absolute enthalpy of formation at 298.15 K has been estimated as 333.9\u00b12 kcal\u2009mol<\/jats:italic><jats:sup><jats:italic>\u22121<\/jats:italic><\/jats:sup> <jats:italic>using the Gaussian\u20103 (G3) procedure. The two species closest in energy to <jats:bold>1T<\/jats:bold> are the triplet H\uf8ffC\uf8ffN\uf8ffN<\/jats:italic><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>ion <jats:bold>2T<\/jats:bold> and the singlet diazirinyl cation <jats:bold>3S<\/jats:bold>, whose G3 enthalpies of formation at 298.15 K are 343.5\u00b12 and 340.6\u00b12 kcal\u2009mol<\/jats:italic><jats:sup><jats:italic>\u22121<\/jats:italic><\/jats:sup><jats:italic>, respectively. Finally, we have discussed the implications of our calculations for the detailed structure of the HCN<\/jats:italic><jats:sub><jats:italic>2<\/jats:italic><\/jats:sub><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>ions formed in the reaction between N<\/jats:italic><jats:sub><jats:italic>3<\/jats:italic><\/jats:sub><jats:sup><jats:italic>+<\/jats:italic><\/jats:sup> <jats:italic>and HCN, experimentally observed by flowing afterglow\u2010selected ion flow\/drift tube mass spectrometry and possibly occurring in Titan's atmosphere.<\/jats:italic><\/jats:p>","DOI":"10.1002\/cphc.200400028","type":"journal-article","created":{"date-parts":[[2004,9,17]],"date-time":"2004-09-17T07:03:10Z","timestamp":1095404590000},"page":"1345-1351","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["A Computational Investigation of HCN<sub>2<\/sub><sup>+<\/sup> Isomeric Structures: Implications for the Chemistry of Titan's Atmosphere"],"prefix":"10.1002","volume":"5","author":[{"given":"Paola","family":"Antoniotti","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Stefano","family":"Borocci","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nicoletta","family":"Bronzolino","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Felice","family":"Grandinetti","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2004,9,17]]},"reference":[{"key":"e_1_2_6_1_2","doi-asserted-by":"publisher","DOI":"10.1006\/icar.2000.6353"},{"key":"e_1_2_6_2_2","doi-asserted-by":"publisher","DOI":"10.1086\/190963"},{"key":"e_1_2_6_3_2","doi-asserted-by":"publisher","DOI":"10.1006\/icar.1995.1002"},{"key":"e_1_2_6_4_2","doi-asserted-by":"publisher","DOI":"10.1063\/1.1734330"},{"key":"e_1_2_6_5_2","doi-asserted-by":"publisher","DOI":"10.1002\/(SICI)1096-9888(199609)31:9<1054::AID-JMS395>3.0.CO;2-0"},{"key":"e_1_2_6_6_2","doi-asserted-by":"publisher","DOI":"10.1063\/1.436354"},{"key":"e_1_2_6_7_2","doi-asserted-by":"publisher","DOI":"10.1063\/1.455573"},{"key":"e_1_2_6_8_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0040-4039(00)74549-7"},{"key":"e_1_2_6_9_2","doi-asserted-by":"publisher","DOI":"10.1021\/jp981150n"},{"key":"e_1_2_6_10_2","doi-asserted-by":"publisher","DOI":"10.1021\/jp983189y"},{"key":"e_1_2_6_11_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0009-2614(00)00259-1"},{"key":"e_1_2_6_12_2","doi-asserted-by":"publisher","DOI":"10.1021\/ja00034a007"},{"key":"e_1_2_6_13_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.19941060120"},{"key":"e_1_2_6_13_3","doi-asserted-by":"publisher","DOI":"10.1002\/anie.199401231"},{"key":"e_1_2_6_14_2","doi-asserted-by":"publisher","DOI":"10.1021\/j100061a032"},{"key":"e_1_2_6_15_2","doi-asserted-by":"publisher","DOI":"10.1021\/j100084a015"},{"key":"e_1_2_6_16_2","doi-asserted-by":"publisher","DOI":"10.1016\/0168-1176(93)03912-6"},{"key":"e_1_2_6_17_2","doi-asserted-by":"publisher","DOI":"10.1039\/C39940002173"},{"key":"e_1_2_6_18_2","doi-asserted-by":"publisher","DOI":"10.1021\/ic00110a007"},{"key":"e_1_2_6_19_2","doi-asserted-by":"publisher","DOI":"10.1002\/chem.19960020507"},{"key":"e_1_2_6_20_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0009-2614(97)01320-1"},{"key":"e_1_2_6_21_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0168-1176(98)00104-9"},{"key":"e_1_2_6_22_2","doi-asserted-by":"publisher","DOI":"10.1002\/(SICI)1521-3765(19981102)4:11<2366::AID-CHEM2366>3.0.CO;2-Z"},{"key":"e_1_2_6_23_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0166-1280(99)00325-5"},{"key":"e_1_2_6_24_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0166-1280(01)00650-9"},{"key":"e_1_2_6_25_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0009-2614(02)01650-0"},{"key":"e_1_2_6_26_2","doi-asserted-by":"publisher","DOI":"10.1016\/S1387-3806(02)00628-0"},{"key":"e_1_2_6_27_2","doi-asserted-by":"publisher","DOI":"10.1002\/jcc.10182"},{"key":"e_1_2_6_28_2","unstructured":"Gaussian\u200998 (Revision\u2009A.7) M. 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