Hyperfine excitation of C2H in collisions with ortho- and para-H2

Accurate estimation of the abundance of the ethynyl (C₂H) radical requires accurate radiative and collisional rate coefficients. Hyperfine-resolved rate coefficients for (de-)excitation of C₂H in collisions with ortho- and para-H₂ are presented in this work. These rate coefficients were computed in time-independent close-coupling quantum scattering calculations that employed a potential energy surface recently computed at the coupled-clusters level of theory that describes the interaction of C₂H with H₂. Rate coefficients for temperatures from 10 to 300 K were computed for all transitions among the first 40 hyperfine energy levels of C₂H in collisions with ortho- and para-H₂. These rate coefficients were employed in simple radiative transfer calculations to simulate the excitation of C₂H in typical molecular clouds.