Rotational excitation cross sections for chloronium based on a new 5D interaction potential with molecular hydrogen

TL;DR

This study provides detailed quantum mechanical calculations of rotational excitation cross sections for chloronium interacting with molecular hydrogen, offering new insights into its collisional behavior in space environments.

Contribution

A new 5D interaction potential for H$_2$Cl$^+$ with H$_2$ was developed, enabling accurate scattering calculations and revealing significant differences from helium-based models.

Findings

Significant differences between H$_2$ and He collision data.

Non-linear scaling trends in cross sections and rate coefficients.

Enhanced understanding of chloronium's collisional excitation in space.

Abstract

Chloronium (H$_2$Cl$^+$) is an important intermediate of Cl-chemistry in space. The accurate knowledge of its collisional properties allows a better interpretation of the corresponding observations in interstellar clouds and therefore a better estimation of its abundance in these environments. While the ro-vibrational spectroscopy of H$_2$Cl$^+$ is well known, the studies of its collisional excitation are rather limited and these are available for the interaction with helium atoms only. We provide a new 5-dimensional rigid-rotor potential energy surface for the interaction of H$_2$Cl$^+$ with H$_2$, calculated from explicitly correlated coupled cluster ab initio theory, which was fitted then with a set of analytical functions, allowing to perform scattering calculations using accurate quantum theories. We analyze the collision-energy-dependence of the rotational state-to-state cross sections and the temperature dependence of the corresponding thermal rate coefficients, with a particular attention on the collisional propensity rules. When comparing our results for collisions with H$_2$ with those obtained with He as a colliding partner, we found very significant differences with non-linear scaling trends, which proves again that He is not a suitable proxy for collisions between hydride molecules and molecular hydrogen, the most abundant gas particle in the interstellar medium.