Hyperfine resolved rate coefficients of HC17O+ with H2 (j=0)

The formyl cation (HCO+) is one of the most abundant ions in molecular clouds and plays a major role in the interstellar chemistry. For this reason, accurate collisional rate coefficients for the rotational excitation of HCO+ and its isotopes due to the most abundant perturbing species in interstellar environments are crucial for non-local thermal equilibrium models and deserve special attention. In this work, we determined the first hyperfine resolved rate coefficients of (HCO+)-O-17 in collision with H-2 (j = 0). Indeed, despite no scattering calculations on its collisional parameters have been performed so far, the (HCO+)-O-17 isotope assumes a prominent role for astrophysical modelling applications. Computations are based on a new four dimensional (4D) potential energy surface obtained at the CCSD(T)-F12a/aug-cc-pVQZ level of theory. A test on the corresponding cross-section values pointed out that, to a good approximation, the influence of the coupling between rotational levels of H-2 can be ignored. For this reason, the H-2 collider has been treated as a spherical body and an average of the potential based on five orientations of H-2 has been employed for scattering calculations. State-to-state rate coefficients resolved for the (HCO+)-O-17 hyperfine structure for temperature ranging from 5 to 100K have been computed using recoupling techniques. This study provides the first determination of (HCO+)-O-17-H-2 inelastic rate coefficients directly computed from full quantum close-coupling equations, thus supporting the reliability of future radiative transfer modellings of (HCO+)-O-17 in interstellar environments.

Automated summary

The formyl cation (HCO+) is abundant in molecular clouds and plays a significant role in interstellar chemistry. This study determined the hyperfine resolved rate coefficients of (HCO+)-O-17 in collision with H-2, providing important data for astrophysical modeling.