Treatment of asymptotic non-adiabatic couplings with higher order reprojection method in the diabatic representation.

The problem of asymptotic non-adiabatic couplings in heavy particle collisions is treated using the reprojection method. The mixing matrix that mixes the asymptotic solutions of the coupled states to obtain appropriate boundary conditions is here derived to second order, yielding a faster convergence of the cross section. In addition, the reprojection method is implemented in a diabatic representation and applied to inelastic scattering of Li + Na and H + H collisions and to mutual neutralization in H+ + H- collisions.

Charge transfer in sodium iodide collisions.

Sodium iodide (NaI) has, over the years, served as a prototype system in studies of non-adiabatic dynamics. Here, the charge transfer collision reactions Na + I ⇆ Na + I (mutual neutralization and ion-pair formation) are studied using an ab initio approach and the total and differential cross sections are calculated for the reactions. This involves electronic structure calculations on NaI to obtain adiabatic potential energy curves, non-adiabatic and spin-orbit couplings, followed by nuclear dynamics, treated fully quantum mechanically in a strictly diabatic representation.

Reactions of C + Cl, Br, and I-A comparison of theory and experiment.

Rate constants for the reactions of C + Cl, Br, and I were measured at 300 K using the variable electron and neutral density electron attachment mass spectrometry technique in a flowing afterglow Langmuir probe apparatus. Upper bounds of <10 cm s were found for the reaction of C with Br and I, and a rate constant of 4.2 ± 1.

Mutual neutralization in collisions of H with Cl.

The cross section and final state distribution for mutual neutralization in collisions of H with Cl have been calculated using an ab initio quantum mechanical approach. It is based on potential energy curves and nonadiabatic coupling elements for the six lowest Σ states of HCl computed with the multireference configuration interaction method. The reaction is found to be driven by nonadiabatic interactions occurring at relatively small internuclear distances (R < 6 a).