A study of the C(D-1)+H-2 -> CH+H reaction: Global potential energy surface and quantum dynamics

The adiabatic global potential energy surface of the CH2 system for the fir st singlet state of A' symmetry ((a) over tilde (1)A') has been computed. A b initio, multireference, single and double configuration interaction calcu lations have been used to characterize this state. This potential energy su rface has a calculated well depth of 99.7 kcal/mol relative to the C(D-1)+H -2 asymptote. The surface has no barrier for the perpendicular C-2v geometr y, but presents a large barrier (12.35 kcal/mol) for the collinear C-infini tyv geometry. The ab initio calculations were carried out over 1748 geometr ies and the resulting energies were fitted to a many body expansion. Based on this surface, we have performed the first quantum reactive scattering ca lculations for the C(D-1)+H-2(X (1)Sigma (+)(g))--> CH(X (2)Pi)+H(S-2) reac tion and total angular momentum J=0. The hyperspherical coordinates time-in dependent method has been used. We note that the state-to-state reaction pr obabilities as a function of the collision energy show a dense resonance st ructure which is unusual for this type of atom+diatom reaction. We present also rotational distributions. (C) 2001 American Institute of Physics.