Isomeric structures of protonated carbon dioxide

✍ Scribed by Ute Seeger; Rolf Seeger; John A. Pople; Paul Von R. Schleyer

• Book ID: 103019546
• Publisher: Elsevier Science
• Year: 1978
• Tongue: English
• Weight: 601 KB
• Volume: 55
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(78)84000-7

✦ Synopsis

Equilibrium structures of protonated carbon dioxide are explored by ab initio molecular orbital theory. The hydroxyearbonyl cation (I) is found to be most stable; the associated proton affinity is calculated to be 130 kcal/rnol, in reasonable agreement withexperimental data. The dioxiryl cation (IV& about 90 kcal[rnot less stable than I, is found to be a seccnd minimum on the potential energy surface. The reaction path connecting isol.lers I and IV appears to involve barriers of signiticant magnitude; consequentIy, it is possible that both HCof and C02Hf may be detecstibge experimentally or serve as reaction intermediates. l-Introduction The structure and energy of protonated carbon dioxide, HCO$ or COzH+, has aroused much interest in several contexts, but there is a lack of agreement both in experimental and in theoretical conclusions. This species may exist in outer space, and should be amenable to radio-frequency observation, provided some information about its structure and rotational frequency would bc available [l-3]. A number of gas phase mass spectroscopic 14-71 and flowing afterglow [8,9] investigations have invoIved HCO$ or CO,H*, but experimental estimates of the heat of formation (or the proton affinity) have varied over a considerable range [4-71. Some authors have been led to suggest that two isomeric forms were being observed [4,5 1. However, the most recently determined proton affiities, 124.0 [7], 125.4 [S], and 128.7 kcal/mol [9], are reasonably consistent. Such gas phase studies do not reveal structure directly, and there has been much speculation regarding this point [4-Q] _