Collisional excitation of isotopologues of carbon monoxide by molecular hydrogen

Abstract

ABSTRACTRate coefficients for transitions between the 14 lowest rotational levels, having energies less than 500 K, of the most abundant isotopologue of carbon monoxide,12C16O, caused by collisions with para-H2 and ortho-H2 are reported for temperatures between 5 and 400 K. These data were computed through time-independent close-coupled scattering calculations employing the high-quality potential energy surface (PES) recently calculated by Faure et al. Rate coefficients for collision-induced transitions are required for radiative transfer modelling of molecules present in interstellar clouds under non-equilibrium conditions. In addition, rate coefficients were computed for other carbon monoxide isotopologues, 13C16O, 12C17O, and 12C18O. The PESs for these systems were obtained by transforming the PES for 12C16O–H2 PES. The rotational transitions of 12C17O isotopologue often display resolved hyperfine structure in astronomical spectra. Rate coefficients for collision-induced transitions between the rotational–hyperfine levels of this isotopologue have been computed by the recoupling technique. A simple radiative transfer calculation was performed to illustrate the utility of using such an approach to relate observed intensities in astronomical spectra with molecular abundances.