Rotational excitation of OH by H2at thermal energies

Abstract

Using a recently computed potential energy surface, the authors calculate cross sections for the rotational excitation of OH by para-H2 (in its rotational ground state) over the range of energies believed to be relevant to the interstellar OH emission. Results are obtained in Hund's case b coupling scheme (neglecting the spin-orbit interaction) and the significance of departures from case b coupling are considered. The authors results indicate that collisions with H2 molecules may be expected to invert the populations of the ground rotational state and of certain excited-state Lambda doublets. At low temperatures (T<or=100K), the inversion mechanism will be quenched by thermalising collisions between the components of the ground-state Lambda doublet.