Theoretical characterization of the potential energy surface of the ground state of the HCO system

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Abstract
Large scale, ab initio configuration interaction calculations are reported on the ground state potential energy surface of the HCO system. The calculated equilibrium geometry of HCO of RCH=1.12 Å, RCO=1.19 Å, and ϑHCO=126° is in good agreement with that determined experimentally, although the calculated H–CO bond strength De=16 kcal/mole is too small by ∼3 kcal/mole. A barrier of 7.5 kcal/mole is found for recombination of H+CO; the height of the barrier is estimated to be too large by 5–6 kcal/mole. The COH isomer, with a calculated equilibrium geometry of ROH=0.98 Å, RCO=1.29 Å, and ϑCOH=114°, is predicted to lie 40 kcal/mole above the HCO isomer, or 24 kcal/mole above the H+CO limit. For COH the barrier for dissociation of 16 kcal/mole is substantially less than that for isomerization (29 kcal/mole) in spite of the fact that isomerization is energetically more favorable. The COH isomer has not yet been identified experimentally. For the HCO system there seems to be no significant difference between the variational and perturbation calculations which have been reported, aside from a constant shift in the energy.

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