Electron impact ro-vibrational transitions and dissociative recombination of H2+ and HD+: Rate coefficients and astrophysical implications

TL;DR

This paper provides new cross sections and rate coefficients for electron-impact ro-vibrational transitions and dissociative recombination of H2+ and HD+ ions, significantly impacting astrochemical models of primordial and molecular cloud environments.

Contribution

It introduces a comprehensive set of quantum defect theory-based calculations for electron-impact processes on H2+ and HD+ ions, improving upon previous data used in astrochemistry.

Findings

New rate coefficients differ significantly from previous estimates.

Updated dissociative recombination rates alter predicted molecular abundances.

Results impact models of primordial gas and shock-induced astrochemistry.

Abstract

Context. Molecular hydrogen and its cation H+2 are among the first species formed in the early Universe, and play a key role in the thermal and chemical evolution of the primordial gas. In molecular clouds, H+2 ions formed through ionization of H2 by particles react rapidly with H2 to form H+3 , triggering the formation of almost all detected interstellar molecules. Aims. We present a new set of cross sections and rate coefficients for state-to-state ro-vibrational transitions of the H+2 and HD+ ions, induced by low-energy electron collisions. Study includes the major electron-impact processes relevant for low-metallicity astrochemistry: inelastic and superelastic scattering, and dissociative recombination. Methods. The electron-induced processes involving H+2 and HD+ are treated using the multichannel quantum defect theory. Results. The newly calculated thermal rate coefficients show significant differences compared to those used in previous studies. When introduced into astrochemical models, particularly for shock-induced chemistry in metal-free gas, the updated dissociative recombination rates produce substantial changes in the predicted molecular abundances. Conclusions. These data provide updated and improved input for the modeling of hydrogen-rich plasmas in environments