Implications of Submillimeter Wave Astronomy Satellite observations for interstellar chemistry and star formation

A long-standing prediction of steady state gas-phase chemical theory is tha t H2O and O-2 are important reservoirs of elemental oxygen and major coolan ts of the interstellar medium. Analysis of Submillimeter Wave Astronomy Sat ellite (SWAS) observations has set sensitive upper limits on the abundance of O-2 and has provided H2O abundances toward a variety of star-forming reg ions. Based on these results, we show that gaseous H2O and O-2 are not domi nant carriers of elemental oxygen in molecular clouds. Instead, the availab le oxygen is presumably frozen on dust grains in the form of molecular ices , with a significant portion potentially remaining in atomic form, along wi th CO, in the gas phase. H2O and O-2 are also not significant coolants for quiescent molecular gas. In the case of H2O, a number of known chemical pro cesses can locally elevate its abundance in regions with enhanced temperatu res, such as warm regions surrounding young stars or in hot shocked gas. Th us, water can be a locally important coolant. The new information provided by SWAS, when combined with recent results from the Infrared Space Observat ory, also provides several hard observational constraints for theoretical m odels of the chemistry in molecular clouds, and we discuss various models t hat satisfy these conditions.