The attractive quartet potential energy surface for the CH3C(a (4)A(2)) + CO reaction

Ab initio molecular orbital (MO) theory, including second-order Moller-Ples set 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 poten tial surface for the reaction of CH3C(a(4)A(2)) with CO. On the quartet sur face, the association barrier is predicted to be only 0.6 kcal mol(-1) at o ur best level of theory [G3(MP2)//QCISD/6-31G(d)]. Rate constants are obtai ned using transition state theory in the temperature range of 300-3000 K. A spin-forbidden electronic deactivation mechanism of CH3C(a(4)A(2)), occurr ing through an intersystem crossing involving a metastable CH3CCO(a(4)A") r adical, is proposed. (C) 2000 Elsevier Science B.V. All rights reserved.