Vibrational level population of H$_2$ and H$_2^+$ in the early Universe

TL;DR

This paper develops a detailed kinetic model for vibrational level populations of H$_2$ and H$_2^+$ in the early Universe, revealing deviations from equilibrium distributions and analyzing the impact of relaxation processes.

Contribution

It introduces a vibrationally resolved chemical network for primordial molecules, including formation, destruction, and relaxation processes, with analytical fits for LTE rate coefficients.

Findings

Vibrational populations deviate from Boltzmann distribution at low redshift.

Relaxation processes significantly influence vibrational level populations.

Provides analytical fits for LTE rate coefficients.

Abstract

We formulate a vibrationally resolved kinetics for molecular hydrogen and its cation in the primordial Universe chemistry. Formation, destruction and relaxation processes for each vibrational level are studied and included as chemical pathways of the present model. The fractional abundance of each vibrational level as a function of the redshift is given: a strong deviation from the Boltzmann distribution is found at low $z$. A discussion of the results is provided, also evaluating the effects of relaxation processes on the level populations. Analytical fits for some LTE rate coefficients are given in the Appendix.