Ab initio characterization of the HCOx (x = -1, 0, +1) species: structures, vibrational frequencies, CH bond dissociation energies, and HCO ionization potential and electron affinity

The potential energy surfaces of the HCOx (x = +1, 0, −1) species near their equilibrium geometries have been calculated employing coupled cluster methods with augmented correlation consistent basis sets. The equilibrium structures, vibrational frequencies, zero point energies, and dissociation energies were computed for all three species. Valence−electron CCSD(T) calculations with the aug-cc-pV5Z basis set predict CH bond dissociation energies, D0, of 140.3 kcal/mol for HCO+, 14.0 kcal/mol for HCO, and 4.5 kcal/mol for HCO-, in good agreement with experiment (140.1 ± 1, 13.9−14.3, and 5.2 ± 0.2 kcal/mol, respectively). The same calculations predict the electron affinity, EA0, and ionization potential, IP0, of HCO to be 7.7 and 187.3 kcal/mol; these values are within 0.5 kcal/mol of the measured values. Inclusion of core−valence correlation corrections has only a minor effect on the calculated energetics.