The hyperfine excitation of OH radicals by He

Abstract

Hyper fine-resolved collisions between OH radicals and He atoms are investigated using quantum scattering calculations and the most recent ab initio potential energy surface, which explicitly takes into account the OH vibrational motion. Such collisions play an important role in astrophysics, in particular in the modelling of OH masers. The hyper fine-resolved collision cross sections are calculated for collision energies up to 2500 cm- 1 from the nuclear spin free scattering S-matrices using a recoupling technique. The collisional hyperfi ne propensities observed are discussed. As expected, the results from our work suggest that there is a propensity for collisions with Δ F = Δ j. The new OH-He hyperfi ne cross sections are expected to signi cantly help in the modelling of OH masers from current and future astronomical observations.