Ion-atom single ionisation at high and intermediate energies

The K-shell ionisation of hydrogen-like atoms in collisions with heavy projectiles is studied in two approximations: the multiple scattering approximation (MS) and the continuum distorted-wave approximation (CDW). A better evaluation of the T-matrix element in the MS approximation is carried out without neglecting the internuclear potential and a simple algebraic connection between this new calculation and the CDW is found. Furthermore, the CDW is modified to provide a better description of the binary electron-projectile collision in the entrance channel through momentum conservation. These approximations and other theoretical methods are compared with experimental results for H++Al, He2++Al, H++He+, H++H, He2++H, Li3++H and Feq++H (q=10, 22) systems. It is found that the MS approach provides better agreement with the experiments for inner-shell ionisation where the projectile charge is small, while the modified CDW gives better values for total cross sections at high projectile charges. The validity of each theoretical method is discussed in terms of the Coulomb charges.