Lyman–α excitation and resonant charge exchange in slow H+–H(1s) collisions

The dominant processes in slow collisions (E < 0.5 keV) of protons and 1s hydrogen atoms are direct elastic scattering, resonant charge exchange, and direct and exchange excitations of H(2p). Differential cross sections have been calculated for all these events by both quantal and classical methods, and characteristics of the resulting Lyman–α (Ly–α) radiation determined.Significant differences from earlier calculations are found for excitation probability, polarization of Ly–α, and the interference oscillations in the charge exchange probability. The phase of the latter is a sensitive function of the interactions causing inelastic scattering. The source of discrepancy with earlier results is the use of the impact parameter approximation (straight-line trajectories); over the range of significant excitation probability, classical path methods using true trajectories give accurate inelastic parameters. Comparison of quantal and classical calculations shows that accurate results for all properties discussed can be obtained by combining classical path calculations of inelastic parameters with semi-classical phase shifts for pure elastic scattering.If polarizations calculated here are used to reinterpret earlier observations of Ly–α emission from 300 eV collisions, the resulting experimental cross sections are not inconsistent with the basic theoretical prediction of equal direct and exchange excitation probabilities.