Photochemistry in a dense manifold of electronic states: Photodissociation of CH₂ClBr

We report electronically nonadiabatic dynamics calculations including spin-orbit coupling for the photodissociation of CH₂ClBr to yield Cl(²P_3/2), Cl(²P_1/2), Br( ²P_3/2), and Br(²P_1/2). The potential energy is a 24 × 24 matrix (divided up here into four 6 × 6 blocks in a first approximation to the problem), in a spin-coupled fully diabatic representation obtained by combining the spin-free fourfold way with single-center spin-orbit coupling constants. The spin-free calculations are carried out by multiconfiguration quasidegenerate perturbation theory, and the fully diabatic potentials including spin-orbit coupling are fit to a matrix reactive force field. The dynamics are carried out by the coherent switches with decay of mixing method in the diabatic representation. The results show qualitative agreement with experiment.