A theoretical study of the isomerization and dissociation processes of theHO-C = O+ ion: interstate crossing in the formation of H-C = O++O

Low energy HO-C=O+ ions [Delta H-f(298) = 142 +/- 2 kcal/mol] uniquely diss ociate to H-C=O+ + O. From ab initio molecular orbital calculations a mecha nism is proposed which involves a 1,2-hydrogen shift of HO-C=O+ ((1)A') to H-CO2+ ((1)A') followed by an interstate crossing leading to a transient tr iplet (3)A " State which then dissociates into H-C=O+ ((1)Sigma) + O (P-3). This mechanism provides a satisfactory explanation of the observed kinetic energy release and it also satisfies the energetic constraints imposed by experiment. From calculations performed at different levels of theory, it b ecame clear that both an advanced level of electronic correlation and large basis sets are a prerequisite for a meaningful description of the above re action. (C) 1999 Elsevier Science B.V.