Semiclassical analytic theory of multi-channel electronic energy transfer in nonadiabatic atomic collisions.

The semiclassical theory of nonadiabatic energy transfer [Adamovich and Rich, J. Chem. Phys. 160, 194101 (2024)] is extended to include multi-channel electronic excitation and quenching in three-dimensional atomic collisions. The transition probabilities, cross sections, and rate coefficients predicted by the theory are compared with high-fidelity quantum scattering predictions for N + N, using state-of-the-art ab initio interaction potentials and nonadiabatic couplings, and with a few available experiments. The theory predictions are in good agreement with quantum scattering, both for conditions where the energy transfer is dominated by a single pair of adiabatic potentials and in cases where the energy transfer is affected by additional intermediate states. These cases include multiple curve crossings encountered during a single collision and pathways with the formation of closed channels, resulting in multiple resonances. The latter case is of particular interest, since it cannot be reduced to the interaction of individual potential pairs. Analytic expressions for the cross sections and rate coefficients are obtained using the same approach as in our previous work. The results quantify the effect of multi-channel interactions on the dynamics of energy transfer in atomic collisions. This approach can also be used to predict rate coefficients for electronic energy transfer in N + O and O + O collisions, as well as other atomic species collisions, such as involving Ar or He, over a wide range of temperatures. The fidelity of the theory predictions depends on the availability of accurate potentials for the interacting excited electronic states and their coupling (both spin-orbit and derivative). The results provide rate coefficients for the predictive simulation of low-temperature plasmas and plasmas generated behind hypersonic shock waves.