Collisional excitation of deuterated hydroxyl (OD) by molecular hydrogen

Abstract

ABSTRACT Cross sections and rate coefficients for transitions between hyperfine levels associated with the 14 lowest rotational/fine-structure levels of OD induced by collisions with ortho-H2 and para-H2 are presented. These collisional parameters have been computed in time-independent close-coupling quantum-scattering calculations with a potential energy surface (PES) describing the OD–H2 interaction, which was obtained by transformation of the OH–H2 PES. Rate coefficients have been computed for temperatures from 5 to 200 K. Cross sections for OD transitions between rotational/fine-structure levels are found to be significantly larger than the corresponding transitions in OH, mainly because of the reduced energy gaps in OD. The hyperfine-resolved rate coefficients were employed in simple radiative transfer calculations for OD and compared with analogous calculations for OH.