Inelastic collisions and recombination between electrons and molecular ions
Inelastic collisions between molecular ions and slow electrons play an important role in naturally occurring ionized media and involve interesting interaction mechanisms which are also under intense theoretical study. Several experiments focused on the collision of small molecular ions with electrons were carried out at the heavy-ion storage ring TSR, located at the Max-Planck-Institut für Kernphysik, Heidelberg. Using the Coulomb explosion imaging technique it was possible to monitor vibrational cooling of the stored homonuclear molecular ions H_2^+ and D_2^+ it could be shown that the cooling is only due to the interaction of electrons with the molecular ions in super-elastic collisions (SEC) where internal energy is transferred to the scattered electron. This process is closely related to dissociative recombination (DR). For the DR and SEC of H_2^+ and D_2^+ ions with near-zero kinetic energy electrons absolute vibrational state specific rate coefficients were measured for the first time. Another series of experiments was focused on the investigation of final fragment states in the DR of LiH^+ and HeH^+. The electronic structure of these ions and the corresponding neutral molecules is such that DR proceeds via a non-adiabatic coupling of electronic and vibrational motion at short internuclear distances. The experiments revealed a dominant population of the highest energetically accessible final fragment states in such reactions. In addition, also the absolute rate coefficient for the DR of LiH^+ molecules with slow electrons was measured.
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