Cold temperatures invert product ratios in Penning ionisation reactions with argon

Abstract

In many chemical reactions with more than one possible outcome, the branching ratio, which is the ratio between the different reaction paths, is nearly constant over a wide range of collision energies. In barrierless systems governed by long-range interactions, however, the branching ratio is more sensitive to collision energy, and its dependence on it can be useful for better understanding the dynamics and reconstructing interaction potentials. Here we present the reaction rates of Penning and associative ionisation of metastable neon and helium with argon atoms. We obtain reaction rates in merge beam experiments, over a wide range of collision energies corresponding to that of room temperature, all the way down to a few millikelvins. We observe a change of two orders of magnitude in the branching ratio in the measured collision energy range and explain these changes using theoretical calculations.

GRAPHICAL ABSTRACT

KEYWORDS:

• Branching ratio
• Cold collisions
• Merged beam
• Penning ionisation
• Associative ionisation

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Natan Bibelnik https://orcid.org/0000-0002-0308-6319

Wojciech Skomorowski https://orcid.org/0000-0002-0364-435X

Additional information

Funding

This work was supported by Israel Science Foundation: [Grant Number 1810/13]; The European Commission: [Grant Number EU-FP7-ERC-CoG 1485]; Alexander von Humboldt foundation.