An improved study of HCO⁺ and He system: Interaction potential, collisional relaxation, and pressure broadening

In light of its ubiquitous presence in the interstellar gas, the chemistry and reactivity of the HCO⁺ ion requires special attention. The availability of up-to-date collisional data between this ion and the most abundant perturbing species in the interstellar medium is a critical resource in order to derive reliable values of its molecular abundance from astronomical observations. This work intends to provide improved scattering parameters for the HCO⁺ and He collisional system. We have tested the accuracy of explicitly correlated coupled-cluster methods for mapping the short- and long-range multi-dimensional potential energy surface of atom-ion systems. A validation of the methodology employed for the calculation of the potential well has been obtained from the comparison with experimentally derived bound-state spectroscopic parameters. Finally, by solving the close-coupling scattering equations, we have derived the pressure broadening and shift coefficients for the first six rotational transitions of HCO⁺ as well as inelastic state-to-state transition rates up to j = 5 in the 5-100 K temperature interval.