Quadrupole association and dissociation of hydrogen in the early Universe

TL;DR

This paper calculates quadrupole transition rates for hydrogen molecules in the early universe, revealing that photodissociation dominates over other destruction mechanisms at certain temperatures, impacting H2 formation models.

Contribution

It provides a comprehensive calculation of quadrupole transition rates and steady-state concentrations of hydrogen molecules, including new formulas for these distributions.

Findings

Quadrupole photodissociation dominates at T ≤ 3000 K.

Rate constants satisfy detailed balance across temperatures.

Steady-state distributions relate to equilibrium distributions.

Abstract

Radiative association and photodissociation rates are calculated for quadrupole transitions of H2. A complete set of bound and unbound states are included in a self-consistent master equation to obtain steady-state concentrations for a dilute system of hydrogen atoms and molecules. Phenomenological rate constants computed from the steady-state concentrations satisfy detailed balance for any combination of matter and radiation temperature. Simple formulas are derived for expressing the steady-state distributions in terms of equilibrium distributions. The rate constant for radiative association is found to be generally small for all temperature combinations. The photodissociation rate constant for quadrupole transitions is found to dominate the rate constants for other H2 photodestruction mechanisms for radiation temperatures less than or equal to 3000 K. Implications for the formation and destruction of H2 in the early universe are discussed.