Vibrational Quenching of Weakly Bound Cold Molecular Ions Immersed in Their Parent Gas

Abstract

Hybrid ion-atom systems provide an excellent platform for studies of state-resolved quantum chemistry at low temperatures, where quantum effects may be prevalent. Here we study theoretically the process of vibrational relaxation of an initially weakly bound molecular ion due to collisions with the background gas atoms. We show that this inelastic process is governed by the universal long-range part of the interaction potential, which allows for using simplified model potentials applicable to multiple atomic species. The product distribution after the collision can be estimated by making use of the distorted wave Born approximation. We find that the inelastic collisions lead predominantly to small changes in the binding energy of the molecular ion.

Inelastic collision dynamics of a single cold ion immersed in a Bose-Einstein condensate

“…While the rate constants for ion-atom-atom TBR in the semi-classical energy regime are comparatively well understood [20], much less is known about the subsequent kinetics of the reaction products, i.e. the kinetics of the produced molecular ions [21,22]. In contrast to extensive studies of ultracold chemistry and inelastic collisions of deeply-bound trapped molecular ions [23][24][25][26][27], TBR produces very weakly bound molecular ions whose dynamics consequently occurs near the molecular dissociation threshold.…”

“…, giving rates for spiralingtype Langevin collisions γ mol L = 2πn at C 4 /µ mol [22]. Here, C 4 = 318.8 a.u.…”

Life and death of a cold BaRb$^+$ molecule inside an ultracold cloud of Rb atoms

“…6) the vibrational quantum number will on average be lowered by one unit at a rate of 1.4 × Γ L . We note that also in a recent theoretical investigation of vibrational quenching collisions of weakly-bound Rb + 2 molecular ions with Rb atoms the changes in the vibrational quantum number are predicted to be small [20].…”

“…A specific property of ion-neutral collisions is the long-range interaction between a charge and an induced dipole, which depends on the interatomic distance as 1/R 4 [18,19]. The combination of long-range interaction and low temperature corresponds to an interesting regime where reactions and inelastic processes can already take place at comparatively large inter-particle distances (see, e.g., [20]). This leads to large cross sections and promotes the formation of weakly-bound molecular states.…”

Electric-field dissociation of weakly bound molecular ions

“…However, these weakly bound molecular ions are experimentally observed, and with it, the validity and accuracy of the classical trajectory method to calculate the three-body recombination rate is corroborated [27,30,32]. After its formation, these molecular ions relax very efficiently into deeper bound vibrational states via collisions with ultracold atoms [33,34] opening up photodissociation routes through the external laser sources characteristic of atomion hybrid traps [32].…”