AVOIDED SURFACE CROSSINGS AND NONADIABATIC EFFECTS IN THE ELECTRONIC QUENCHING REACTION LI(P-2)+HCL-]LICL+H(S-2)

The electronically nonadiabatic reactive quenching reaction (Li(P))-P-2 + HCl --> LiCl + (H(S))-S-2 is studied using ab initio state-averaged multiconfiguration self-consistent field/configuration interaction wave functions. A seam of avoided crossings of the 1,2(2)A' potential energy surfaces is determined directly, that is, without prior determination of the individual potential energy surfaces. The seam is parametrized in terms of the approximate entrance channel reaction coordinate R, the distance from Li to the center of mass of HCI, and reported for the range R = 6.0-3.55a0. This range includes the portion of the seam that is exoergic relative to the reactant channel, (Li(P))-P-2 + HCl, asymptote. First derivative nonadiabatic coupling matrix elements are computed in the vicinity of the seam to characterize the propensity for nonadiabatic transitions.