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Nature 274, 456 - 457 (03 August 1978); doi:10.1038/274456a0

Role of different isomers of the H2CN+ ion in the formation of interstellar HCN and HNC


Department of Chemistry, University of California, Berkeley, California 94720

THE H2CN+ molecular ion is generally agreed1–4 to have a critical role in the formation of interstellar HCN and HNC. The obvious problem that H2CN+ has not yet been identified in interstellar space is complicated by considerable uncertainty due to the possible existence of three distinct isomers of H2CN+, with nuclear arrangements Brown4 stated that although the third isomer had been completely neglected in previous discussion, it is likely to have a crucial role in the formation of HNC. Brown also notes that the linear isomer, which is isoelectronic with acetylene and thus expected to lie lowest of all the isomers of H2CN+, may play no part at all in the formation of either HCN or HNC. This is from the hypothesis that the sequence thought most likely to lead to HCN isCH3+N+right arrowH2CN++H (4)orCH3 ++Nright arrowH2CN++H (5)followed by dissociative recombinationH2CN++eright arrowHCN+H (6)Brown argues that the formation of the more stable linear isomer (1) would require the migration of a hydrogen atom from carbon to nitrogen. As this migration is expected to be very costly energetically, the H2CN+ on the right hand side of reactions (4) and (5) should be the isomer (2) above. Similarly, he argues that the sequence leading to HNCC++NH3right arrowH2CN++H (7)H2CN++eright arrowHNC+H (8)should exclusively involve isomer (3). We report here theoretical studies designed to investigate the molecular structure of (3) and its energy relative to the previously studied3 isomers (1) and (2). In addition, because reactions (4), (5) and (7) must be exothermic or very nearly so if they play a part in the interstellar medium, this question has also been assessed.



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