A study of the C(1D)+H2→CH+H reaction:: Global potential energy surface and quantum dynamics

The adiabatic global potential energy surface of the CH2 system for the first singlet state of A' symmetry ((a) over tilde (1)A') has been computed. Ab initio, multireference, single and double configuration interaction calculations have been used to characterize this state. This potential energy surface 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 geometry, but presents a large barrier (12.35 kcal/mol) for the collinear C-infinityv geometry. The ab initio calculations were carried out over 1748 geometries and the resulting energies were fitted to a many body expansion. Based on this surface, we have performed the first quantum reactive scattering calculations for the C(D-1)+H-2(X (1)Sigma (+)(g))--> CH(X (2)Pi)+H(S-2) reaction and total angular momentum J=0. The hyperspherical coordinates time-independent method has been used. We note that the state-to-state reaction probabilities as a function of the collision energy show a dense resonance structure which is unusual for this type of atom+diatom reaction. We present also rotational distributions. (C) 2001 American Institute of Physics.