# Quantum mechanical study of the high-temperature $\mathrm{H}^+ + \mathrm{HD} \to \mathrm{D}^+ + \mathrm{H}_2$ reaction for the primordial universe chemistry

## TL;DR

This study employs quantum mechanics to analyze the high-temperature H+ + HD reaction, providing detailed cross sections and rate coefficients relevant for primordial universe chemistry, highlighting the reaction's dependence on initial states and vibrational levels.

## Contribution

It presents the first comprehensive quantum-mechanical calculations of state-to-state reaction rates for H+ + HD at high temperatures, considering various vibrational and rotational states.

## Key findings

- Rate coefficients vary significantly with initial rotational states below 4000 K.
- Reaction probability decreases with higher final vibrational levels.
- Reaction dynamics depend on whether the process is endothermic or exothermic.

## Abstract

We use the time-independent quantum-mechanical formulation of reactive collisions in order to investigate the state-to-state $\mathrm{H}^+ + \mathrm{HD} \to \mathrm{D}^+ + \mathrm{H}_2$ chemical reaction. We compute cross sections for collision energies up to 1.8 electron-volts and rate coefficients for temperatures up to 10000 kelvin. We consider HD in the lowest vibrational level $v=0$ and rotational levels $j=0$ to 4, and H$_2$ in vibrational levels $v'=0$ to 3 and rotational levels $j'=0$ to 9. For temperatures below 4000 kelvin, the rate coefficients strongly vary with the initial rotational level $j$, depending on whether the reaction is endothermic ($j\le 2$) or exothermic ($j\ge 3$). The reaction is also found less and less probable as the final vibrational quantum number $v'$ increases. Our results illustrate the importance of studying state-to-state reactions, in the context of the chemistry of the primordial universe.