THE PRODUCTION OF CONDENSED-PHASE CO IN QUIESCENT MOLECULAR CLOUDS

The high abundance of condensed phase CO in cool quiescent molecular c louds is not reproducible by our standard two-phase and three-phase ga s-grain chemical models. We consider changes to the models designed to enhance the predicted abundance of condensed phase CO. We find that t he use of the so-called ''highmetal'' elmental abundances to describe the initial composition of the gas leads to higher condensed phase CO abundances, which are in better agreement with observation, by reducin g the surface hydrogenation rate of CO into methanol (CH3OH). We also confirm, however, that high-metal elemental abundances depress the gas phase production of complex organic molecules. This problem can be re moved by using initial conditions with metallic elements, especially s ulfur, predominantly on grain surfaces rather than in the gas.