Semiclassical analytic theory of electronic energy transfer in 3D atomic collisions

A previously developed semiclassical theory of nonadiabatic energy transfer is used to analyze electronic excitation and quenching in three-dimensional atomic collisions. The predicted transition probabilities, cross sections, and rate coefficients are compared with the quantum scattering calculations for O + O and N + N, for the same interaction potentials and nonadiabatic coupling, and with the experimental data where available. The theory predictions are in very good agreement with quantum scattering, at the conditions when the energy transfer is dominated by a single pair of adiabatic potentials. Closed-form analytic expressions for the cross sections and rate coefficients are obtained, for both the strongly and weakly coupled cases. The results quantify and illustrate the effect of the interaction potentials and their coupling on the energy transfer. The analytic cross sections and rate coefficients are in good agreement with the numerical predictions. The same approach has been used to predict the rate coefficients of electronic excitation and quenching in collisions of N + O atoms. The fidelity of these predictions may be improved considerably if accurate potentials for the excited electronic states of N + O and their coupling are available. The applicability of the semiclassical theory for the prediction of the rates of heavy particle impact excitation in atom-molecule collisions is discussed.