Projectile charge dependence of ionization and fragmentation of CO in fast collisions

Single and multiple ionization cross sections of CO have been measured as a function of the projectile charge. The experiment was carried out at fixed collision energies of 1 MeV amu(-1) using the coincidence time-of-flight technique. The cross sections increase rapidly for small q and more slowly for large q. The branching ratios of all the transient molecular ions and the kinetic energy distribution of the dissociating transient CO2+ exhibit similar projectile charge dependence. These observed trends are explained quite satisfactorily using a simple model based on perturbation theory and the independent electron approximation. The model predicts that the average value of the projectile-electron interaction strength in collisions resulting in target ionization varies quickly for small q and more slowly for large q.