Electron impact ro-vibrational transitions and dissociative recombination of H ₂ ⁺ and HD ⁺

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 H 2 by particles react rapidly with H 2 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 (RVT) of the H 2 + and HD + ions, induced by low-energy electron collisions. The study includes the major electron-impact processes relevant for low-metallicity astrochemistry: inelastic and superelastic scattering, and dissociative recombination (DR). Methods . The electron-induced processes involving H 2 + and HD + were treated using the multichannel quantum defect theory (MQDT). 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 DR 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 where a high abundance of free electrons is expected, such as planetary nebulae, HII regions, and the ionospheres of giant planets.