Rotationally inelastic scattering of OH by molecular hydrogen: Theory and experiment

We present an experimental and theoretical investigation of rotationally inelastic transitions of OH, prepared in the X ²Π, v = 0, j = 3/2 F₁ f level, in collisions with molecular hydrogen (H₂ and D₂). In a crossed beam experiment, the OH radicals were state selected and velocity tuned over the collision energy range 75–155 cm^-1 using a Stark decelerator. Relative parity-resolved state-to-state integral cross sections were determined for collisions with normal and para converted H₂. These cross sections, as well as previous OH–H₂ measurements at 595 cm^-1 collision energy by Schreel and ter Meulen [J. Chem. Phys. 105, 4522 (1996)], and OH–D₂ measurements for collision energies 100–500 cm^-1 by Kirste et al. [Phys. Rev. A 82, 042717 (2010)], were compared with the results of quantum scattering calculations using recently determined ab initio potential energy surfaces [Ma et al., J. Chem. Phys. 141, 174309 (2014)]. Good agreement between the experimental and computed relative cross sections was found, although some structure seen in the OH(j = 3/2 F₁ f → j = 5/2 F₁ e) + H₂(j = 0) cross section is not understood