Hyperfine excitation of 13CCH and C13CH by collisions with para-H2

The computation of hyperfine resolved cross sections and rate coefficients for open-shell molecules in collision with H-2 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 (CCH)-C-13 and (CCH)-C-13 isotopologues induced by collisions with para-H-2. These calculations have been performed using a recently published C2H-H-2 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.