Close-coupling approach to differential ionization in ion-atom collisions

Ion-atom collisions take place in astrophysical and laboratory plasmas. Therefore, accurate knowledge of excitation, electron-capture and ionisation processes occurring in such collisions plays an important role in practical applications. A wave-packet convergent close-coupling approach is capable of providing benchmark data on the integrated and differential cross sections for all processes taking place in such collisions. The approach expands the scattering wavefunction using a two-center pseudostate basis. This allows one to account for all underlying processes, namely, direct scattering and ionisation, and electron capture into bound and continuum states of the projectile. The wave packets are used to discretize the continuum. The generated pseudostates are used in the expansion of the total scattering wave function. The approach gives the integrated, fully differential, as well as various doubly and singly differential cross sections for ionization of atomic targets. It has recently been applied to p-He collisions. Calculations of ionization cross sections differential in the electron emission energy, in the emission angle, as well as in the scattered-projectile angle have been performed in the intermediate energy region where coupling between various channels and electron-electron correlation effects are important. The results agree well with experimental data, where available. Moreover, our calculations reveal an interesting interplay between direct ionization and electron capture into the continuum. We show that the ionization cross section differential in the angle of the ejected electron is dominated by electron capture into the continuum for ejection into small angles, while ejection into large angles is purely due to direct ionization.