Ion chemistry in the early universe: revisiting the role of HeH+ with new quantum calculations

TL;DR

This paper uses new ab initio quantum calculations to reassess the abundance of HeH+ in the early universe, finding it more abundant than previously thought and enhancing prospects for its detection.

Contribution

It introduces new quantum reaction rates for HeH+ with H, improving the accuracy of early universe chemical models and comparing its role with LiH+.

Findings

HeH+ abundance is over ten times higher with new rates.

Enhanced potential for detecting cosmological signatures of HeH+.

Provides detailed quantum reaction cross sections and rate coefficients.

Abstract

The role of HeH+ has been newly assessed with the aid of newly calculated rates which use entirely ab initio methods, thereby allowing us to compute more accurately the relevant abundances within the global chemical network of the early universe. A comparison with the similar role of the ionic molecule LiH+ is also presented. Quantum calculations have been carried out for the gas-phase reaction of HeH+ with H atoms with our new in-house code, based on the negative imaginary potential method. Integral cross sections and reactive rate coefficients obtained under the general conditions of early universe chemistry are presented and discussed. With the new reaction rate, the abundance of HeH+ in the early universe is more than one order of magnitude larger than in previous studies. Our more accurate findings further buttress the possibility to detect cosmological signatures of HeH+.