Cl+ and HCl+ in Reaction with H2 and Isotopologues: A Glance into H Abstraction and Indirect Exchange at Astrophysical Conditions

TL;DR

This study investigates the reaction mechanisms of Cl+ and HCl+ ions with H2 and isotopologues at cryogenic temperatures, revealing hydrogen abstraction as the dominant process and providing insights into astrochemical spin-state chemistry.

Contribution

It provides experimental data on reaction rates and mechanisms of Cl+ and HCl+ with H2 isotopologues at astrophysical temperatures, highlighting hydrogen abstraction over full scrambling.

Findings

Reaction rates are mostly temperature-independent.

HCl+ + H2 reactions proceed via hydrogen abstraction.

No isotopic exchange observed for H2Cl+ ion.

Abstract

Astrochemical models of interstellar clouds, the sites of stars, and planet formation require information about spin-state chemistry to allow quantitative comparison with spectroscopic observations. In particular, it is important to know if full scrambling or H abstraction (also known as proton hopping) takes place in ion-neutral reactions. The reaction of Cl+ and HCl+ with H2 and isotopologues has been studied at cryogenic temperatures between 20 and 180 K using a 22 pole radio frequency ion trap. Isotopic exchange processes are used to probe the reaction mechanism of the HCl+ + H2 reaction. The results are compared with previous measurements and theoretical predictions. The rate coefficients for the Cl+ + H2 and HCl+ + H2 reactions are found to be constant in the range of temperatures studied, except for the DCl+ + D2 reaction, where a weak negative temperature dependence is observed, and reactions with D2 are found to be significantly slower than the Langevin rate. No isotopic exchange reactions are observed to occur for the H2Cl+ ion. The analysis of the products of the HCl+ + H2 isotopic system clearly indicates that the reaction proceeds via simple hydrogen atom abstraction.