A quasi-molecular mechanism of formation of hydrogen in the early Universe -- a scheme of calculation

TL;DR

This paper proposes a detailed calculation scheme for the formation of hydrogen via a quasi-molecular mechanism involving $H_2^+$ ions during the early Universe's recombination era, aiming to improve cosmological models.

Contribution

It develops a comprehensive calculation scheme for free-bound radiative transitions into $H_2^+$ states, enhancing the modeling of early Universe recombination processes.

Findings

Scheme enables fast, complete cosmological recombination modeling

Incorporates transitions into highly excited $H_2^+$ states

Supports improved understanding of hydrogen formation in early Universe

Abstract

In our recent papers (Kereslidze et all 2019a, 2021) a non-standard quasi-molecular mechanism was suggested and applied to treat the cosmological recombination. It was assumed that in the pre-recombination stage of evolution of the Universe an electron combined with two neighbouring protons and created the hydrogen molecular ion, $H_2^+$ in highly excited states, which then descended into the lower-lying states or dissociated. In this work, we elaborate the scheme of calculation for free-bound radiative transitions into attractive states of $H_2^+$ as functions of redshift $z$. Together with the earlier developed treatment of bound-bound radiative transitions in $H_2^+$, the elaborated scheme of calculation can be used for the design of a fast and complete cosmological recombination code.