REFINED CALCULATIONS OF THE STRUCTURES AND STABILITIES OF THE FORMYL (HCO+) AND ISOFORMYL (COH+) CATIONS

High-level (QCISD(T)/6-311 + G(3df, 2p)) ab initio molecular orbital calculations have been used to obtain the structures and stabilities of the formyl (HCO+) and isoformyl (COH+) cations. The best predicted structures have r(e)(C-O) = 1.105 angstrom and r(e)(C-H) = 1.093 angstrom for HCO+, and r(e)(C-O) = 1. 154 angstrom and r(e)(O-H) = 0.989 angstrom for COH+. The best estimates of the heats of formation (DELTA-H(f298)) for COH+ and HCO+ are 987 and 824 kJ mol-1, respectively, leading to an energy difference between them of 163 kJ mol-1.