Fast LiH destruction in reaction with H: quantum calculations and astrophysical consequences

TL;DR

This study uses quantum mechanical calculations to determine the reaction rates of LiH with hydrogen, revealing rapid destruction of LiH in the early Universe, which impacts its observability in cosmic background radiation.

Contribution

The paper provides first-principles quantum calculations of LiH destruction rates, confirming previous predictions and clarifying its rapid depletion in early Universe conditions.

Findings

LiH is rapidly destroyed in the early Universe between redshifts 400 and 100.

The fractional abundance of LiH is drastically reduced due to this rapid depletion.

LiH is unlikely to be observed in the cosmic background radiation due to its quick destruction.

Abstract

We present a quantum-mechanical study of the exothermic 7LiH reaction with H. Accurate reactive probabilities and rate coefficients are obtained by solving the Schrodinger equation for the motion of the three nuclei on a single Born-Oppenheimer potential energy surface (PES) and using a coupled-channel hyperspherical coordinate method. Our new rates indeed confirm earlier, qualitative predictions and some previous theoretical calculations, as discussed in the main text. In the astrophysical domain we find that the depletion process largely dominates for redshift (z) between 400 and 100, a range significant for early Universe models. This new result from first-principle calculations leads us to definitively surmise that LiH should be already destroyed when the survival processes become important. Because of this very rapid depletion reaction, the fractional abundance of LiH is found to be drastically reduced, so that it should be very difficult to manage to observe it as an imprinted species in the cosmic background radiation (CBR). The present findings appear to settle the question of LiH observability in the early Universe. We further report several state-to-state computed reaction rates in the same range of temperatures of interest for the present problem.