Impact of a quasi-molecular mechanism of cosmological recombination on the population of the 2s-level of hydrogen

Abstract

ABSTRACT The population of the 2s-level of hydrogen formed in the early Universe is studied within a standard and a non-standard quasi-molecular mechanism of recombination. We demonstrate that, if hydrogen molecular ion $H_2^+$ temporarily formed during a collision directly dissociates into a hydrogen atom and a proton, both mechanisms of recombination lead to the same probabilities of population. These probabilities differ significantly, however, when attractive quasi-molecular channels are uninvolved and only repulsive channels remain in the treatment. The probabilities of the direct and indirect radiative transitions into the 2s-level of hydrogen are evaluated. The dominant process in the population of 2s-level of hydrogen is the direct free–bound radiative transition.