Unveiling shape resonances in H + HF collisions at cold energies

TL;DR

This study reveals how shape resonances significantly affect the rotational quenching rates of HF molecules by hydrogen at cold interstellar temperatures, and demonstrates how molecular alignment can disentangle these resonances.

Contribution

It introduces a method to analyze and decompose shape resonances in cold H + HF collisions by manipulating molecular alignment, revealing the role of total angular momentum.

Findings

Resonances cause up to two-fold increase in thermal rate coefficients at low temperatures.

Alignment of HF rotational angular momentum allows decomposition of resonance peaks.

Manifolds of resonances arise from specific combinations of orbital and total angular momentum.

Abstract

Resonances are associated with the trapping of an intermolecular complex, and are characterized by a series of quantum numbers such as the total angular momentum and the parity, representative of a specific partial wave. Here we show how at cold temperatures the rotational quenching of HF(j=1,2) with H is strongly influenced by the presence of manifolds of resonances arising from the combination of a single value of the orbital angular momentum with different total angular momentum values. These resonances give rise up to a two-fold increase in the thermal rate coefficient at the low temperatures characteristic of the interstellar medium. Our results show that by selecting the relative geometry of the reactants by alignment of the HF rotational angular momentum, it is possible to decompose the resonance peak, disentangling the contribution of different total angular momenta to the resonance.