Quenching of molecular rotations and vibrations at ultracold temperatures

N. Balakrishnan, A. Dalgarno

We report quantum mechanical scattering calculations of zero temperature quenching rate coefficients for vibrationally and rotationally excited O 2 in collisions with 3 He. It is found that vibrational energy is channeled into more specific rotational levels in the ultracold regime than at thermal energies where a broad range of rotational levels are populated. The influence of the van der Waals interaction on the low-temperature quenching rate coefficients and the possibility of trapping vibrationally excited O 2 by the buffer gas cooling technique are also discussed.

Tim Langen, Giacomo Valtolina, Dajun Wang +1 more

N. Balakrishnan, A. Dalgarno

Alessandro Volpi, John L. Bohn

We have calculated cross sections for vibrational quenching in collisions of O217(X 3∑g−) with He3 at cold and ultracold temperatures, explicitly accounting for the electronic spin degree of freedom. The observed population of the final spin-rotational levels can be interpreted on the basis of useful “propensity rules” governing the intensity of the collision-induced transitions. In addition, it is found that the orientation of the molecular spin is reasonably robust against collisional relaxation, even in vibrationally excited states. This finding implies that magnetic trapping of vibrationally excited, but rotationally and translationally cold, molecules may be possible.

Qingze Guan, D. Blume, Vincent M. Klinkhamer +3 more

N. Balakrishnan, Gerrit C. Groenenboom, Roman V. Krems +1 more

We present cross sections for rotational, vibrational, and fine-structure transitions in He–CaH(2Σ) collisions at cold and ultracold temperatures calculated using the ab initio potential energy surface reported in the preceding paper. Rotational quenching is fast, vibrational quenching is slow. The spin-rotational interaction, although small and having no influence at temperatures above 10 K, changes significantly the rate coefficients for rotational quenching at lower temperatures. The theoretical rotational, vibrational, and elastic cross sections are compared with the results of a buffer gas cooling experiment carried out at a temperature of about 0.4 K. The theoretical predictions for the vibrational and elastic cross sections are larger than the measured values. The sensitivity to the potential energy surface is explored. A modified surface diminishes but does not remove the differences between theory and experiment.