Model studies of intersystem crossing effects in the O + H₂ reaction

We use quantum scattering and trajectory surface hopping methods to examine the influence of intersystem crossing between the lowest energy triplet and singlet states on the O(³P) + H₂ reaction dynamics. Several two-state reaction path models of the potential energy surfaces and spin-orbit coupling are studied. In these models, the triplet state curve shows a barrier along the reaction path and the singlet state a well such that the two states intersect at a location near the barrier top. Eleven choices of the parameters in the Hamiltonian are examined in which the effect of the triplet-singlet crossing location, the singlet well depth, and the size and coordinate dependence of the spin-orbit coupling are varied. The quantum calculations show that if the crossing occurs on the reagent side of the triplet barrier, and the spin-orbit coupling at that point is similar to what exists in the reagent O atom, then the low energy reactivity is dominated by intersystem crossing.