Classical-trajectory Monte Carlo calculations for energetic electron-capture processes

Electron-capture processes of a proton from a hydrogen atom are studied at a collision energy of 5 MeV by the classical-trajectory Monte Carlo method. Thomas double-scattering processes and knock-on captures, which are characteristic of high-energy ion-atom collisions, are detected in a two-dimensional treatment. Another type of capture that takes place through a momentum-matching mechanism is also investigated. Three-body effects modify these processes considerably in some cases from the idealized pictures given in a simplified treatment of successive two-body collisions published before [see, e.g., R. Shakeshaft and L. Spruch, Rev. Mod. Phys. 51, 369 (1979)]. Three-dimensional calculations designed for knock-on captures are also performed, and the cross section, 1.9×${10}^{\mathrm{-}29}$ ${\mathrm{cm}}^2$, is in good agreement with quantum-mechanical calculations.