Theory of interstellar molecules

Abstract

Various estimates are described for the rate of formation of hydrogen molecules on the surface of interstellar grains in H 1 regions. The average abundance of molecular hydrogen relative to atomic hydrogen remains uncertain by a few orders of magnitude.Possibilities are presented for the formation of OH molecules (and, more briefly, for other diatomic molecules), either on the surface of dust grains or by exchange reactions in the interstellar gas after cloud-cloud collisions. The rate for photodissociation of OH in H 1 regions is uncertain.A brief discussion is given of various possible mechanisms for maser action in the OH molecule, such as optical pumping of microwave levels by UV radiation at the edge of an H 11 region. It appears that the narrow OH emission lines must originate in cool gas bordering an H 11 region.