2018MNRAS.475.5480D

We investigate here the excitation of methylidene (CH) induced by collisions with atomic and molecular hydrogen (H and H₂). The hyperfine-resolved rate coefficients were obtained from close coupling nuclear-spin-free scattering calculations. The calculations are based upon recent, high-accuracy calculations of the CH(X²Π)-H(²S) and CH(X²Π)-H₂ potential energy surfaces. Cross-sections and rate coefficients for collisions with atomic H, para-H₂, and ortho-H₂ were computed for all transitions between the 32 hyperfine levels for CH(X²Π) involving the n <= 4 rotational levels for temperatures between 10 and 300 K. These rate coefficients should significantly aid in the interpretation of astronomical observations of CH spectra. As a first application, the excitation of CH is simulated for conditions in typical molecular clouds.