Importance of rotationally inelastic processes in low-energy Penning ionization of CHF$_3$

TL;DR

This study demonstrates that rotationally inelastic processes significantly influence low-energy Penning ionization of CHF$_3$, highlighting the importance of including rotational excitation probabilities in reaction models for accurate predictions.

Contribution

It provides the first experimental and theoretical analysis of rotationally inelastic effects in cold polyatomic molecule collisions, emphasizing their crucial role in reaction dynamics.

Findings

Rotationally inelastic collisions are essential in low-energy reaction dynamics.

Quantum defect theory accurately models the reaction cross sections when rotational excitation is included.

Classical scaling laws are insufficient to describe the observed phenomena.

Abstract

Low energy reaction dynamics can strongly depend on the internal structure of the reactants. The role of rotationally inelastic processes in cold collisions involving polyatomic molecules has not been explored so far. Here we address this problem performing a merged-beam study of the He*+CHF$_3$ Penning ionization reaction in a range of collision energies $E/k_B$=0.5--120 K. The experimental cross sections are compared with total reaction cross sections calculated within the framework of the quantum defect theory. We find that the broad range of collision energies combined with the relatively small rotational constants of \chfs makes rotationally inelastic collisions a crucial player in the total reaction dynamics. Quantitative agreement between theory and experiment is only obtained if the energy-dependent probability for rotational excitation is included in the calculations, in stark contrast to previous experiments where classical scaling laws were able to describe the results.