A uniform quasi-classical description of radiative transitions for asymmetric rare-gas atom-atom collisions

Abstract

The uniform quasi-classical approximation [14] is used to describe the optical spectra formed during asymmetric collisions between atoms of rare gases in which one of the atoms is in a metastable state. We consider the reactions He(2¹ S) + Ne → He(1¹S) + Ne + ħω and Ar(³ P ₂) + He → Ar(¹S) + He + ħω, in which the optical transition mechanisms are typical of most rare gases. Quasi-molecular terms of excited states and radiative widths calculated in a unified semiempirical approach are used. Spectral characteristics are calculated for thermal collision energies in the entire frequency range, including the center and both wings of the forbidden line. For the blue wing, our results are consistent with the widely used Condon approximation at collision energies E ≥200 cm⁻¹. At lower collision energies and in the region of the red wing and center of the forbidden line, the spectral distributions that cannot be described in the Condon approximation are reproduced in the uniform quasi-classical approximation. Comparison with quantum-mechanical calculations by the strong-coupling method confirms the high accuracy of the uniform quasi-classical approximation in the entire range of radiation frequencies.