Measurement of the vibrational populations of molecular ions and its application to dissociative recombination in storage rings

Dissociative recombination of HD+ in selected vibrational quantum states

Rate coefficients for dissociative recombination of HD+ in selected vibrational states have been measured by a combination of two molecular fragment imaging methods by using the heavy-ion storage ring technique. Recombination fragment imaging yields state-to-state reaction rates. These rates are converted to rate coefficients by using vibrational level populations of the stored ion beam, derived from nuclear coordinate distributions measured on extracted ions. The results show strongly increasing rate coefficients for high vibrational excitation, where additional dissociation routes open up, in agreement with a theoretical calculation. Very low rate coefficients are found for certain, isolated vibrational states.

DISSOCIATIVE RECOMBINATION WITH ION STORAGE RINGS

The development of heavy-ion storage-cooler rings for atomic physics has made it possible to produce high-quality beams of molecular ions that are internally cold. The stored molecular-ion beam is immersed in a cold electron bath, which gives a beam of low divergence and small cross-sectional area. The electron cooler also serves as a target for electron-molecular ion collision experiments. This allows the study of dissociative recombination of cold molecules with respect to cross sections, branching ratios, and angular distributions at an unprecedented luminosity.