# Non-thermal photons and direct photodissociation of H2, HD and HeH+ in the chemistry of the primordial Universe

## TL;DR

This paper calculates the impact of non-thermal photons from primordial recombination on the photodissociation rates of key molecules like H2, HD, and HeH+ in the early Universe, revealing new effects on chemical abundances.

## Contribution

It introduces new calculations of photodissociation rates including non-thermal photons from primordial recombination, enhancing understanding of early Universe chemistry.

## Key findings

- Non-thermal photons significantly affect molecular photodissociation rates.
- New fits for HeH+ photodissociation rates by thermal photons are provided.
- Chemical abundances are altered by the inclusion of non-thermal photon effects.

## Abstract

Non-thermal photons deriving from radiative transitions among the internal ladder of atoms and molecules are an important source of photons in addition to thermal and stellar sources in many astrophysical environments. In the present work the calculation of reaction rates for the direct photodissociation of some molecules relevant in early Universe chemistry is presented; in particular, the calculations include non-thermal photons deriving from the recombination of primordial hydrogen and helium atoms for the cases of H2, HD and HeH+. New effects on the fractional abundances of chemical species are investigated and the fits for the HeH+ photodissociation rates by thermal photons are provided.