Rovibrational transitions in HCl due to collisions with H₂

In this work, we present scattering calculations of HCl with H$_2$ using a new full-dimensional potential energy surface. State-to-state rate coefficients for rovibrational transitions were calculated using a quantum close-coupling method for vibrational quenching in HCl(v₁=1, j₁)+H₂(v₂=0, j₂) → HCl(v₁^'=0, j₁^')+H₂(v₂^'=0, j₂^' ) collisions, with j₁=0-5. Rate coefficients ranging from 5 to 1000 K are presented for both para-H₂ (j₂=0) and ortho-H₂ (j₂=1) collision partners. A 5D coupled-states (5D-CS) approximation was used to determine rate coefficients, which were benchmarked against the close-coupling results. Since the 5D-CS approximation reduces the computational time, it was used to extend the database of transitions to include HCl states with v₁ = 0 - 2 with j₁ up to 30 for temperatures between 10 K and 3000 K.Hyperfine-resolved rate coefficients for rovibrational transitions of HCl were determined by using a recoupling approach and the 5D-CS T-matrices. HCl has been detected in the atmospheres of some planets, as well as in interstellar clouds. It is an important tracer of chlorine, and the rates presented here will allow a better determination of the HCl abundance in the interstellar medium and an improved understanding of interstellar chlorine chemistry.