Molecular collisions in ultracold atomic gases

Abstract

It has recently become possible to form molecules in ultracold gases of trapped alkali metal atoms. Once formed, the molecules may undergo elastic, inelastic and reactive collisions. Inelastic and reactive collisions are particularly important because they release kinetic energy and eject atoms and molecules from the trap. The theory needed to handle such collisions is presented and recent quantum dynamics calculations on ultracold atom-diatom collisions of spin-polarised Li + Li2, Na + Na2 and K + K2 are described. All these systems have potential energy surfaces on which barrierless atom exchange reactions can occur, and both inelastic and reactive rates are very fast (typically k inel > 10 −10 cm 3 s −1 in the Wigner regime).

Reactions of ultracold alkali-metal dimers

“…However, a full treatment of the dynamics of these reactions would require a detailed study of the potential energy surfaces for at least the two lowestlying electronic states and the interactions between them. This contrasts with the situation for reactions involving spinstretched states of alkali-metal atoms and triplet dimers, which have been studied using single electronic surfaces for the quartet states of the trimers [35][36][37][38][39][40]. Li 3759 4145 3979 3910 3660 Na 2539 3843 3281 3287 2962 K 1639 2611 2460 2444 2264 Rb 1393 2421 2266 2295 2101 Cs 965 1974 1943 1981 1958 Our atomization energies for homonuclear systems may be compared with 13,436 cm −1 for Li 3 from multireference configuration interaction (MRCI) calculations [41], and 5437.1 cm −1 for Cs 3 from full configuration interaction (CI) calculations [42].…”

“…If both species are in their absolute ground state, inelastic collisions are impossible, but there remains the possibility of reactive collisions. Indeed, for fermionic 40 K 87 Rb, Ospelkaus et al [11] have carried out detailed studies of the exothermic atom exchange reaction,…”

Cold atomic and molecular collisions: approaching the universal loss regime

“…In cases where the uncertainty is 1 to 5%, which is more typical, it is sufficient to span many oscillations in the cross-sections in a plot such as figure 8. Under these circumstances it is not meaningful to regard the results of scattering calculations on a single potential as predictions for the physical system, and it is essential to understand the range of results that may be obtained across the uncertainties in the potential [28,29]. It is clear from figure 8 that the range of possible results is very large for purely elastic collisions in the s-wave regime, but diminishes both when loss is present (for initial > j 0) and when there are significant contributions from several partial waves [26].…”

Potential energy surface for spin-polarized rubidium trimer

“…3 However, the successful control of such chemistry requires intimate knowledge of the corresponding atom+ dimer ͑and dimer+ dimer͒ collision processes. 4 In these studies, the trimer potential energy surfaces have played a crucial part because the correct description of quantum dynamics at ultralow energies requires the potential energy surface to be complete and to exhibit correct long-range behavior.…”