Collisional Excitation of Carbon Monoxide in Interstellar Clouds

Different models for the collisional excitation of carbon monoxide (CO) have been investigated by solving the rate equations for the 10 lowest energy levels, including stimulated emission and absorption by S K isotropic radiation, spontaneous emission, and collisions. The results are qualitatively applicable to other linear molecules. They show that a wide range of rotational excitation temperatures, including population inversions, can be produced by the various kinetic temperatures and particle densities which are likely to occur in the interstellar regions containing molecules.