Rotational excitation of small carbon chains by collisions with He in the ISM

Abstract

Abstract. Modeling of molecular emission from interstellar clouds requires the calculation of rate coefficients for excitation by collision with the most abundant species. Based on new highly correlated potential energy surfaces, rotational excitation of C2H and C2H− radicals in collision with He are investigated. C2H fine and hyperfine structure is taken into account. As already found for other systems, rate coefficients for the C2H − ion are larger by a factor up to 3 compared to the neutral species.