2023MNRAS.526..885P

The determination of physical conditions in interstellar clouds requires reliable estimation of radiative and collisional data for molecules detected in space. In this work, rate coefficients for de-excitation of C₂H and C₂D induced by collisions with both ortho- and para-H₂ are presented. Calculations have been carried out using a recently published four-dimensional C₂H-H₂ potential energy surface. Fine-structure resolved cross-sections were computed with the time-independent close-coupling approach. We report cross-sections for transitions between the first 41 levels of C₂H and corresponding rate coefficients up to 500 K. We also computed cross-sections for transitions between the first 31 levels of C₂D and corresponding rate coefficients up to 200 K. Then, hyperfine structure resolved cross-sections and rate coefficients were computed using the recoupling technique. The hyperfine structure resolved rate coefficients for C₂H-H₂ and C₂D-H₂ are calculated for the first 38 hyperfine C₂H energy levels and first 55 hyperfine C₂D energy levels both for temperatures up to 100 K. These collisional data were used in a simple radiative transfer modelling.