2023MNRAS.523.3732P

The computation of hyperfine resolved cross sections and rate coefficients for open-shell molecules in collision with H₂ is a true methodological and numerical challenge. Such collisional data are however required to interpret astrophysical observations. We report the first hyperfine resolved rate coefficients for (de-)excitation of ¹³CCH and C¹³CH isotopologues induced by collisions with para-H₂. These calculations have been performed using a recently published C₂H-H₂ potential energy surface. Hyperfine resolved cross sections and rate coefficients between the first 98 energy levels of the two isotopologues were determined using a recoupling technique for temperatures ranging from 5 to 100 K. Significant isotopic substitution effects were found, showing the necessity of computing isotopologue specific collisional data. These rate coefficents have then been used in a simple radiative transfer modelling for typical molecular cloud conditions.