The attractive quartet potential energy surface for the CH3C(a 4A2)+CO reaction Original Research Article

Ab initio molecular orbital (MO) theory, including second-order Møller–Plesset perturbation theory (MP2), complete active space self-consistent-field (CASSCF), and quadratic configuration interaction (QCISD) methods have been applied for the study of the CH3CCO energy hypersurface. The energetics of various species on both quartet and doublet surfaces are calculated at the G3(MP2) level. Theoretical calculations reveal an attractive quartet potential surface for the reaction of CH3C(a 4A2) with CO. On the quartet surface, the association barrier is predicted to be only 0.6 kcal mol−1 at our best level of theory [G3(MP2)//QCISD/6-31G(d)]. Rate constants are obtained using transition state theory in the temperature range of 300–3000 K. A spin-forbidden electronic deactivation mechanism of CH3C(a 4A2), occurring through an intersystem crossing involving a metastable CH3CCO(a 4A″) radical, is proposed.