Unravelling the stereodynamics of cold HD-H2 collisions

TL;DR

This paper combines first-principles quantum scattering simulations with experimental data to reveal how a specific shape resonance influences the stereodynamics of cold HD-H2 collisions at around 1 Kelvin.

Contribution

It provides the first detailed simulation matching experimental angular distributions, highlighting the role of a shape resonance in cold molecular collisions.

Findings

Identification of a dominant L=2 shape resonance affecting scattering

Demonstration of stereodynamical control through partial wave analysis

Validation of quantum scattering calculations with experimental data

Abstract

Measuring inelastic rates with partial wave resolution requires temperatures close to a Kelvin or below, even for the lightest molecule. In a recent experiment Perreault et al. [1] studied collisional relaxation of excited HD molecules in the v = 1, j = 2 state by para- and ortho-H2 at a temperature of about 1 K, extracting the angular distribution of scattered HD in the v = 1,j = 0 state. By state-preparation of the HD molecules, control of the angular distribution of scattered HD was demonstrated. Here, we report a first-principles simulation of that experiment which enables us to attribute the main features of the observed angular distribution to a single L = 2 partial-wave shape resonance. Our results demonstrate important stereodynamical insights that can be gained when numerically-exact quantum scattering calculations are combined with experimental results in the few-partial-wave regime.