Interactions and cold collisions of AlF in the ground and excited electronic states with He

TL;DR

This paper investigates the interactions and collisions of AlF molecules with helium using advanced quantum chemistry, providing insights crucial for optimizing buffer-gas cooling techniques for ultracold AlF gases.

Contribution

It develops accurate potential energy surfaces for AlF-He interactions using high-level ab initio methods and assesses the impact on collision cross-sections and resonance positions.

Findings

Low sensitivity of cross-sections to PES variations

Uncertainty in shape resonance positions

Results aid in improving buffer-gas cooling of AlF

Abstract

Aluminium monofluoride (AlF) is a promising candidate for laser cooling and the production of dense ultracold molecular gases, thanks to its relatively high chemical stability and diagonal Frank-Condon factors. In this study, we examine the interactions and collisions of AlF in its $X^1\Sigma^+$, $a^3\Pi$, and $A^{1}\Pi$ electronic states with ground-state He using state-of-the-art \textit{ab initio} quantum chemistry techniques. We construct accurate potential energy surfaces (PESs) employing either the explicitly correlated coupled-cluster CCSD(T)-F12 method augmented by the CCSDT correction or the multireference configuration-interaction method for higher-excited electronic states. Subsequently, we employ these PESs in coupled-channel calculations to determine the scattering cross-sections for AlF+He collisions and bound states of the complex. We estimate the uncertainty of the calculated PESs and apply it to assess the uncertainty of the scattering results. We find a relatively low sensitivity of the cross-sections to the variation of the PESs, but the positions of shape resonances remain uncertain. The present results are relevant for further improvements and optimizations of buffer-gas cooling of AlF molecules.