Detailed experimental and theoretical study of collision-induced dissociation of ${\mathrm{Na}}_2^{+}$ ions on He and ${\mathrm{H}}_2$ targets at keV energies

A combined experimental and theoretical investigation of collision-induced dissociation (CID) of the quasi-one-electron system ${\mathrm{Na}}_2^{+}$ He at 80 eV center-of-mass energy is presented. This study, complemented by additional measurements with an ${\mathrm{H}}_2$ target, provides a detailed analysis of the competition between the two basic CID mechanisms: via excitation of electronic states of the ${\mathrm{Na}}_2^{+}$ molecular ion and via momentum transfer to one of the ${\mathrm{Na}}^{+}$ core. The experimental method is based on a combined coincidence and time-of-flight technique, resulting in a complete measurement of the velocity vectors of the two fragments and giving a full determination of the collision parameters. The theoretical analysis is based on the so-called nonadiabatic quantum molecular dynamics, developed recently. This theory treats self-consistently and simultaneously classical atomic motion and quantum electronic transitions in dynamical processes of atomic many-body systems using time-dependent density functional theory. It allows one to simulate the experiment in microscopic detail and, thus, provides a deep insight into the excitation and dissociation mechanism. The combined theoretical and experimental analysis can later be extended to more complex systems like larger molecules or clusters.