Reactivity of the F spin–orbit excited state in the F + HD reaction: Product translational and rotational energy distributions

Abstract

We report fully-quantum calculations of product translational energy distribution functions for the F + HD → FH + D, FD + H reactions. We include all three potential energy surfaces and all couplings (non-adiabatic, spin–orbit, and Coriolis) between them. Comparisons with the experimental results by Liu and co-workers (F. Dong, S. H. Lee and K. Liu, J. Chem. Phys., 2000, 113, 3633) confirm the relatively low reactivity of spin–orbit excited state (F*) atoms. At low collision energies formation of HF(v′ = 3) products is allowed only for reaction of F*. Once energetically allowed, the reactivity of the F ground state dominates. Excellent agreement with experiment is obtain under the assumption of an F*:F concentration ratio of 0.16:0.84 in the molecular beam, which corresponds to a thermal equilibrium of the two spin–orbit states at the experimental temperature (600 K). From the accurate calculation of the F* reactivity and its relatively small contribution to the overall reactivity of the reaction, we attribute discrepancies between calculation and experiment to an inadequacies in the simulation of the reactivity of the F ground state, likely a result of the residual errors in the ground electronic potential energy surface. In addition, we compare the predicted HF(v′ = 3) rotational distributions from reaction of F* at E_c = 0.6 kcal mol⁻¹ with the experimental results of Nesbitt and co-workers (W. W. Harper, S. A. Nizkorodov and D. J. Nesbitt, J. Chem. Phys., 2002, 116, 5622). Good agreement is seen.