Radiative electron capture in proton-hydrogen collision

The 1s-1s proton-hydrogen radiative electron capture is studied within the nonrelativistic semiclassical approximation. Several three-particle theoretical methods currently used in collision theory are applied. Double, single, and total cross sections are computed. The continuum distorted-wave method is found to present a projectile angular distribution with two critical angles, i.e., two enhancements, which can be physically visualized in terms of combined processes of a mechanical collision followed (or preceded) by an interaction with the radiation field. It is shown that for high projectile velocities, the contribution of these critical angles to the total cross section is negligible. Prior and post impulse approximations are also calculated.