Rovibrational transitions in OH due to collisions with He

In this work, we present scattering calculations for rovibrational transitions of OH(X²Π) induced by collisions with He in which fine-structure and Λ-doubling are incorporated dynamically. Rate coefficients for rotationally inelastic transitions of OH(v=0) induced by He have been computed previously for j≤11.5 [Klos et al., Chem. Phys. Lett, 445, 12 (2007)]. The present work extends previous calculations to include rates for vibrational de-excitation from OH(v=1,j). A quantum close-coupling method was used for selected j at temperatures between 1 and 500 K. The coupled-states approximation, which is less computationally intensive, was used for j=0.5-10.5 for temperatures between 1 and 3000 K; these rates were benchmarked against the close-coupling results.

The hydroxyl radical is a key species in the water chemistry of star-forming regions, and recent observations from the James Webb Space Telescope include spectra corresponding to the fundamental OH rovibrational band. The state-to-state rate coefficients presented here are needed to interpret spectra taken from non-local thermodynamic equilibrium (NLTE) environments.