THE ATTRACTIVE QUARTET POTENTIAL-ENERGY SURFACE FOR THE CH(A (4)SIGMA-)- A ROLE FOR THE A (4)A'' STATE OF THE KETENYL RADICAL IN COMBUSTION(CO REACTION )

Ab initio quantum mechanical techniques,including the self-consistent- field (SCF), single and double excitation configuration interaction (C ISD), single and double excitation coupled cluster (CCSD), and the sin gle, double, and perturbative triple excitation coupled cluster [CCSD( T)] methods have been applied for the study of the HCCO(a 4A'') energy hypersurface. Rate constant measurements suggest an attractive potent ial for the reaction of CH(a 4SIGMA-) with CO. A vanishingly small ene rgy barrier is predicted here in the CH(a 4SIGMA-) + CO reaction chann el. We propose that a spin-forbidden electronic deactivation of CH(a 4 SIGMA-) might occur through an intersystem crossing involving the a 4A '' state of HCCO. The energetics and the geometries of the reactants a nd products on both quartet and doublet energy surfaces are presented. The relationship between this research and experimental combustion ch emistry is explored.