Elastic and glancing-angle rate coefficients for heating of ultracold Li and Rb atoms by collisions with room-temperature noble gases, H_2, and N_2

Published

January 6, 2023

Author(s)

Jacek Klos, Eite Tiesinga

Abstract

Trapped ultracold alkali-metal atoms can be used to measure pressure in the UHV and XHV pressure regimes, those with p<10^-6} Pa. This application for ultracold atoms relies on precise knowledge of collision rate coefficients of alkali-metal atoms with residual room-temperature atoms and molecules in the ambient vacuum or with deliberately introduced gasses. Here, we determine combined elastic and inelastic rate coefficients as well as glancing-angle rate coefficients for ultracold Li and Rb with room-temperature noble-gas atoms as well as H_2 and N_2 molecules. Glancing collisions are those processes where only little momentum is transferred to the alkali-metal atom and this atom is not ejected from its trap. Rate coefficients are found by performing quantum close-coupling scattering calculations using \em ab-initio} ground-state electronic Born-Oppenheimer potential energy surfaces. The potentials for Li and Rb with noble gas atoms and also for Rb-H_2 and Rb-N_2 systems are based on the non-relativistic spin-restricted coupled-cluster method with single, double and noniterative triple excitations (RCCSD(T)). For Li-N_2 the potential is computed at the explicitly correlated spin-restricted RCCSD(T)-F12 level. For Rb, Kr, and Xe atoms, scalar relativistic corrections to the core electrons have been included while second-order spin-orbit corrections from the valence electrons have been estimated. Data for Li-H_2 and Li-He were taken from the existing literature. We estimate standard uncertainties of the rate coefficients by comparing rate coefficients calculated using potentials found with electronic basis sets of increasing size, including estimates of relativistic spin-orbit corrections and the uncertainty of the van-der-Waals coefficients. The relative uncertainties of rate coefficients are 1%-2% with the exception of Li or Rb colliding with Ne. Those have relative uncertainties of 9\% and 8%, respectively.We also show that a commonly used semiclassical approximation for the total elastic rate coefficient agrees with the quantum calculations to 10% with the exception of Li and sions with H_2, where the semiclassical value underestimates the quantum value by 20%.

Citation

The Journal of Chemical Physics

Volume

158

Pub Type

Journals

Download Paper

https://doi.org/10.1063/5.0124062

Local Download

Keywords

UHV pressure, laser-cooled atoms, collisional rate coefficients

Citation

Klos, J. and Tiesinga, E. (2023), Elastic and glancing-angle rate coefficients for heating of ultracold Li and Rb atoms by collisions with room-temperature noble gases, H_2, and N_2, The Journal of Chemical Physics, [online], https://doi.org/10.1063/5.0124062, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935431 (Accessed April 1, 2026)