ROTATIONAL QUENCHING OF CO DUE TO H₂COLLISIONS

Abstract

Rate coefficients for state-to-state rotational transitions in CO induced by\nboth para- and ortho-H$_2$ collisions are presented. The results were obtained\nusing the close-coupling method and the coupled-states approximation, with the\nCO-H$_2$ interaction potential of Jankowski & Szalewicz (2005). Rate\ncoefficients are presented for temperatures between 1 and 3000 K, and for\nCO($v=0,j$) quenching from $j=1-40$ to all lower $j^\\prime$ levels. Comparisons\nwith previous calculations using an earlier potential show some discrepancies,\nespecially at low temperatures and for rotational transitions involving large\n$|\\Delta j|$. The differences in the well depths of the van der Waals\ninteractions in the two potential surfaces lead to different resonance\nstructures in the energy dependence of the cross sections which influence the\nlow temperature rate coefficients. Applications to far infrared observations of\nastrophysical environments are briefly discussed.\n