Theoretical studies of intersystem crossing effects in the O(~3P,~1D)+H_2 reaction

摘要

We have studied the influence of intersystem crossing on the reaction dynamics of the O+H_2 reaction by performing trajectory surface hopping (TSH)calculations with accurate potential-energy surfaces and global spin-orbit coupline surfaces that we have generated using a four state model proposed by Hoffmann and Schatz.In the TSH calculations,we develop a new mized representation that treats the reactant and product asymptotes in the adiabatic representation,and the singlet-triplet crossing region in the diabatic representation.This representation thus correctly describes O and OH fine structure-resolved cross sections,and it also treats intersystem crossing effects arising from the singlet-triplet crossing.Our calculations are based on the 1~3A' and 1~3A'' states of Walch and Kuppermann,and athe 1~1a'state of Dobbyn and Knowles.The globally determined spin-orbit coupling matrix is derived from complete active apace space self-consistent dield calcualtions suing the two-electron Breit-Jauli Hamiltonian.Our dynamics calculations show that the triplet O+H~2 cross section is modestly increased (up to 20% at collision energies >10 Kcal/mol above the reactive threshold)by intersystem crossing,and product rotational excitational excitation is also increased.In addition,we find that the OH spin-orbit distributions favor the ~2II_3/2 state by a 2:1 ratio over ~2II_1/2.This result is consistent with observations for O atom reactions with alkanes.