Heidelberg 2015 – scientific program
MO 17.1: Invited Talk
Thursday, March 26, 2015, 11:00–11:30, PH/HS1
State-selective attachment of helium atoms to stored, cold molecular ions — •Sandra Brünken, Lars Kluge, Alexander Stoffels, Oskar Asvany, and Stephan Schlemmer — I. Physikalisches Institut, Universität zu Köln, Germany
Helium atoms attach to molecular cations via inversely temperature-dependent ternary association processes, forming weakly bound (<3 kcal/mol) He-M+ complexes. We investigate the kinetics of this process by storing a few thousand mass-selected ions in a temperature-variable cryogenic rf 22-pole ion trap in the presence of a high number density of He and following the temporal evolution of Hen-M+ complexes (n<6). In this way the rate coefficients for ternary association and collision induced dissociation are obtained for a number of ions, e.g. H3+, CH5+, CD+, CF+, CO+, HCO+. The dependence of the ternary association rate coefficient on the vibrational and rotational excitation of the ions is observed. A detailed account of the underlying kinetics will be presented on the example of rotational excitation of CD+. This state-dependent complex formation rate is employed for sensitive action spectroscopy of the parent and complex ions [1,2]. Its apparent general applicability will be demonstrated with recent examples of high-resolution IR spectroscopy (LIICG - Laser Induced Inhibition of Complex Growth), and of purely rotational spectroscopy. In addition first results of IR pre-dissociation spectroscopy of stored He-M+ complexes will be presented.
 Asvany et al., Applied Physics B 114, 203 (2014);  Brünken et al., ApJL 783, L4 (2014)