The Production of Condensed Phase CO in Quiescent Molecular Clouds

The high abundance of condensed phase CO in cool quiescent molecular clouds is not reproducible by our standard two-phase and three-phase gas-grain chemical models. We consider changes to the models designed the enhance the predicted abundance of condensed phase CO. We find that the use of the so-called 'high-metal' 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 reducing 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 removed by using initial conditions with metallic elements, especially sulfur, predominantly on grain surfaces rather than in the gas.