Fine-structure resolved rovibrational transitions for SO + H2 collisions

Cross sections and rate coefficients for sulfur monoxide (SO) + H-2 collisions are calculated using a full six-dimensional (6D) potential energy surface (PES). The coupled states (CS) approximation is used to compute fine-structure resolved cross sections for rovibrational transitions between states with v = 0-2, where v is the vibrational quantum number of the SO molecule. The CS calculations for Delta v = 1 are benchmarked against close-coupling (CC) results for spin-free interactions. For Delta v = 0, the present fine-structure resolved CS results are benchmarked against existing CC results obtained with a rigid rotor approximation. In both cases, the agreement is found to be satisfactory, which suggests that the present results may provide reliable estimates for fine-structure resolved rovibrational transitions. These estimates are the first of their kind based on a full 6D PES. Rate coefficients are reported for temperatures between 10 K and 3000 K for both para- and ortho-H-2 colliders. A comparison of the para-H-2 rates with mass-scaled results for He shows substantial differences that may be important in astrophysical models.