Ion-atom differential cross sections at intermediate energies

The classical-trajectory Monte Carlo method has been used to calculate H++H(1s) electron-capture and ionization differential cross sections in the range 25--200 keV. The results indicate the importance of including excited product states to describe the small-angle electron-capture scattering. Angular scattering of the electron removed by the ionization process has been studied as a function of ejected-electron velocity v/sub e/. The classical calculations are in reasonable agreement with coupled-channel results of Shakeshaft [Phys. Rev. A 18, 1930 (1978)] as to the ''electron capture to the continuum'' (ECC) component of the ionization process where this term is defined as the ejected electron being more closely centered to the projectile than the target nucleus after the collision. The ECC cross section sigma/sub ECC/ was studied as a function of collision energy (50--500 keV/amu) and projectile charge state (q = 1--10). At high energies, sigma/sub ECC/ scales as q/sup 2.3//E/sup 2.5/. The maximum value for sigma/sub ECC/ was determined to be an energy E/sub max/approx. =(56 keV/amu)q/sup 0.4/. Restricting the ECC component to small electron-scattering angles, theta/sub lab/< or =50, and electron-ejection velocities v/sub e/ = v/sub p/(1.0 +- 0.1), where v/sub p/ is the projectile velocity, indicates this process is a minor component of the total ionization cross section at intermediate energies