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

The energies of six stationary points on the ${\mathrm{OH+CO\to HOCO\to H+CO}}_{\mathrm{2}}$ potential energy surface have been calculated using the G3 and CBS-QB3 methods. An analysis combining ab initio and experimental enthalpies yielded ${\mathrm{\Delta H}}_f^{\text{298\hspace{0.05em}}\mathrm{K}}$ $\mathrm{(trans-}\mathrm{HOCO}\text{)=−42.9±1.5\hspace{0.05em}}{\mathrm{kcal mol}}^{\mathrm{-1}}$ $\text{(−43.8±1.4\hspace{0.05em}}{\mathrm{kcal mol}}^{\mathrm{-1}})$ at the G3(CBS-QB3) level of theory. These results confirm the revised HOCO heat of formation derived from photoionization spectroscopy and suggest that the HOCO potential well is $\text{8.8\hspace{0.05em}}{\mathrm{kcal mol}}^{\mathrm{-1}}$ shallower than previously thought. We discuss the implications of these results for accurate Rice–Ramsperger–Kassel–Marcus modeling or quantum mechanical scattering calculations of the $\mathrm{OH+CO}$ reaction. © 2000 American Institute of Physics.