The HCO2 potential energy surface: Stationary point energetics and the HOCO heat of formation

The energies of six stationary points on the OH+CO --> HOCO --> H+CO2 poten tial energy surface have been calculated using the G3 and CBS-QB3 methods. An analysis combining ab initio and experimental enthalpies yielded Delta H -f(298 K) (trans-HOCO)=-42.9 +/- 1.5 kcal mol(-1) (-43.8 +/- 1.4 kcal mol(- 1)) at the G3(CBS-QB3) level of theory. These results confirm the revised H OCO heat of formation derived from photoionization spectroscopy and suggest that the HOCO potential well is 8.8 kcal mol(-1) shallower than previously thought. We discuss the implications of these results for accurate Rice-Ra msperger-Kassel-Marcus modeling or quantum mechanical scattering calculatio ns of the OH+CO reaction. (C) 2000 American Institute of Physics. [S0021-96 06(00)32437-0].