Association between projectile and target excitation in slow Ar$^{q+}$-CO$_2$ collisions

Abstract

We investigate ionic fragmentation of CO$_2^{n+}$~\mbox{($2\le n\le 4$)} produced in collisions with Ar$^{q+}$~\mbox{($4\le q\le 16$)} projectiles at a collision velocity of $\approx$~0.3~a.u. For most projectile and fragmentation channel combinations, the shape of the kinetic energy release distribution (KERD) differs with the electron capture mediated charge change (\mbox{$\Delta q$}) in the scattered projectile: KERD for \mbox{$\Delta q = 2$} is broader at high KER than for \mbox{$\Delta q =1$}. The difference generally diminishes with increasing projectile charge. Two deviations in this general trend are seen in the fragmentation of CO$_2^{3+}$, one for Ar$^{4+}$ impact in the high KER region and the other for Ar$^{6+}$ impact in the low KER region. The calculated reaction windows for multielectron capture within the framework of the extended classical over-the-barrier model (ECOBM) indicate that while ionization of the target occurs via multielectron capture, the scattered projectile may subsequently undergo multi-fold autoionization. Interpreting projectile autoionization to be a consequence of capture into highly excited states and high fragment KER to be a consequence of excitation of the ionized target to high-lying states, we find a strong dependence between the target and scattered projectile excitations.