Computing rotational energy transfers of OD⁻/OH⁻in collisions with Rb: isotopic effects and inelastic rates at cold ion-trap conditions

Abstract

We report close-coupling (CC) quantum dynamics calculations for collisional excitation/deexcitation of the lowest four rotational levels of OD − and of OH − interacting with Rb atoms in a cold ion trap. The calculations are carried out over a range of energies capable of yielding the corresponding rates for state-changing events over a rather broad interval of temperatures which cover those reached in earlier cold trap experiments. They involved sympathetic cooling of the molecular anion through a cloud of laser-cooled Rb atoms, an experiment which is currently being run again through a Heidelberg-Innsbruck collaboration. The significance of isotopic effects is analysed by comparing both systems and the range of temperatures examined in the calculations is extended up to 400 K, starting from a few mK. Both cross sections and rates are found to be markedly larger than in the case of OD − /OH − interacting the He atoms under the same conditions, and the isotopic effects are also seen to be rather significant at the energies examined in the present study. Such findings are discussed in the light of the observed trap losses of molecular anions.

Collision-driven state-changing efficiency of different buffer gases in cold traps: He(1S), Ar(1S) and p-H2(1Σ) on trapped CN−(1Σ)

“…The standard time-independent formulation of the Coupled-Channel (CC) approach to quantum scattering will not be repeated in detail (see for example Taylor 30 for a general formulation) since we have already discussed it in many of our earlier works. [31][32][33] Hence, only a short outline will be given.…”

Modeling Quantum Kinetics in Ion Traps: State‐changing Collisions for OH+() Ions with He as a Buffer Gas

“…Rather good agreement was found there with the quantum modeling of the relevant dynamics and with our quantitative estimate of the involved collisional rates. The same molecular anions OH − /OD − , were further computationally modeled under similar conditions in a cold ion trap containing sympathetically cooled Rb atoms, thereby providing further information on the size and efficiency of the molecular cooling processes for its rotational levels under different environments.…”

Ab initio study of reactive collisions between Rb(2S) or Rb(2P) and OH−(1Σ+)

“…In such an environment, elastic, inelastic and reactive collisions can take place, leading to a loss of ions if the kinetic energy release exceeds the depth of the a) Electronic mail: milakas@ulb.ac.be trap or if the ions lose their charge. The co-trapping of Rb and OH − has been the subject of several theoretical studies [9][10][11][12][13] and is currently under experimental investigation by the HAItrap group in the university of Heidelberg from which the first results have been published 14 . This system is of particular interest since the dynamics of anions, specially at low temperature, can exhibit non-standard behaviour 15 .…”