Classical four-body calculations of⁴He⁺+H and H+H collisions

Electron transfer and ionisation are calculated by a four-body classical-trajectory Monte-Carlo method for collisions of hydrogenic ions with H(1s). Results for electron capture by 35 keV to 1 MeV 4 He + are in good agreement with recent data. For both 4 He + (1s) and H(1s) projectiles the classical electron-exchange contribution to single ionisation peaks at a lower impact energy than that of direct ionisation and makes the projectile electron-loss cross section peak near the maximum in the data. No classical bound state of H - was produced in any of the several thousand trajectories followed; however, metastable situations, which eventually yielded ionisation events, were encountered. By a classical Coulomb scaling law, the present results also apply to a certain class of Rydberg-atom (or ion)+Rydberg-atom collisions.