Ultracold quantum dynamics: Spin-polarizedK+K2collisions with three identical bosons or fermions

Abstract

We have developed a potential-energy surface for spin-polarized K͑ 2 S͒ +K 2 ͑ 3 ⌺ u + ͒ collisions and carried out quantum dynamical calculations of vibrational quenching at low and ultralow collision energies for both bosons 39 K and 41 K and fermions 40 K. At collision energies above about 0.1 mK the quenching rates are well described by a classical Langevin model, but at lower energies a fully quantal treatment is essential. We find that for the low initial vibrational state considered here ͑v =1͒, the ultracold quenching rates are not substantially suppressed for fermionic atoms. For both bosons and fermions, vibrational quenching is much faster than elastic scattering in the ultralow-temperature regime. This contrasts with the situation found experimentally for molecules formed via Feshbach resonances in very high vibrational states.

Formation of molecular oxygen in ultracoldO+OHcollisions

“…Similar conclusions have been found by Lara et al [43,44] for collisions between OH molecules with Rb atoms. The relatively large rate coefficient for the reaction in the zero-temperature limit indicates that barrierless exothermic reactions occur at significant rates at ultracold temperatures, in agreement with similar results for alkali-metal atom -diatom reactions [21,22,23,24,25,26,27,28,29]. Fig.…”

“…This model has been shown to work quite well for a certain range of collision energy, for atomexchange reactions such as K + K 2 [23], Li + Li 2 [24], and also for non-reactive Rb + OH collisions [43,44]. We have shown [31] that the Langevin model predicts rate coefficients in close agreement with experimental values for Rb + Rb 2 [8], Cs + Cs 2 [10,11], and Rb/Cs + RbCs [13] collisions reported recently.…”

“…The typical rate coefficients of these reactions are on the order of 10 −11 − 10 −10 cm 3 molecule −1 s −1 depending on the collisional system, the temperature and the vibrational levels probed. All these experimental studies indicate that inelastic and reactive processes occur at significant rates at ultracold temperatures, in accordance with theoretical predictions on barrier reactions [15,16,17,18,19,20] as well as a number of alkali-metal atom -dimer systems [21,22,23,24,25,26,27,28,29,30] such as Li + Li 2 , Na + Na 2 and K + K 2 which proceeds without an energy barrier in the entrance channel. The alkali-metal systems are characterized by triatomic complexes with deep potential wells which make them challenging systems for accurate quantum calculations.…”

“…At E c = 10 −6 K the reactive rate coefficient is two orders of magnitude larger than the elastic one. This is reminiscent of other exothermic barrierless systems such as alkali-metal atom -diatom collisions [21,22,23,24,25,26,27,28,29]. At energies between E c = 0.01 K and 30 K, elastic and reactive rate coefficients are of comparable magnitude.…”

Reaching the cold regime: S(1D) + H2 and the role of long-range interactions in open shell reactive collisions

“…Regarding the former, the Wigner threshold laws provide a behaviour for the l cross-section below the centrifugal barrier given by E l−1/2 . If, after the barrier were overcome, the reaction probability reached quickly the limit value of one, the behaviour should follow a 1/k 2 dependence, that is ∼ E −1 [67][68][69]. This would result as a "bump" in the cross-sections.…”