A theoretical study of the reaction between N+(P-3) and formaldehyde and related processes in the gas phase

The [H-2, C, N, O](+) potential energy surface (PES) in its triplet state m ultiplicity has been explored by means of high-level ab initio calculations , carried out in the framework of the G2 theory. From the PES survey we con clude that some of the products of the N+(P-3) + H2CO reaction are the resu lt of a competitive dissociation of the H2CON+ cation into NO+ + H2C or N H2CO+. Although the first process is moro exothermic than the second one, it involves a conical intersection, and as a consequence N + H2CO+ are the dominant products. NH + HCO+, which are also experimentally observed produc ts, can be formed either by the dissociation of the HCONH+ cation, through another conical intersection, or by the fragmentation of a quite stable HN . . . HCO+ complex. Other possible products, such as CNH + OH+, HCN + OH+, and CO + NH2+, although exothermic, should not be observed since the corres ponding reaction pathways involve high activation barriers. These conclusio ns are in good agreement with the experimental evidence. The topology of th e [H-2, C, N, O](+) PES also explains why no reaction is observed when NH2 and CO or CH2 and NO+ interact in the gas phase, while in CH2+ + NO reacti ons, only the charge exchange channel is open. We also predict that the dom inant products in OH+ + HCN reactions should be NH + HCO+. However, when th is reaction involves the CNH isomer the observed products should be not onl y NH + HCO+ but also NH2+ + CO.