Temperature-dependent rotationally inelastic collisions of OH- and He

TL;DR

This study investigates the rotational relaxation and excitation of OH- ions colliding with helium at cryogenic temperatures, providing experimental rate coefficients and comparing them with quantum calculations to understand collision dynamics.

Contribution

It presents the first experimental measurement of inelastic collision rates of OH- with helium at low temperatures and compares these with quantum scattering calculations.

Findings

Experimental collision rates increase with temperature.

Good agreement between experiment and theory within accuracy.

Discrepancies in temperature dependence trends.

Abstract

We have studied the fundamental rotational relaxation and excitation collision of OH- J=0 <-> 1 with helium at different collision energies. Using state-selected photodetachment in a cryogenic ion trap, the collisional excitation of the first excited rotational state of OH- has been investigated and absolute inelastic collision rate coefficients have been extracted for collision temperatures between 20 and 35 K. The rates are compared with accurate quantum scattering calculations for three different potential energy surfaces. Good agreement is found within the experimental accuracy, but the experimental trend of increasing collision rates with temperature is only in part reflected in the calculations.