Unusual Low-Temperature Reactivity of Water: The CH + H2O Reaction as a Source of Interstellar Formaldehyde?

Water is an important reservoir species for oxygen in interstellar space and plays a key role in the physics of star formation through cooling by far-infrared emission. While water vapor is present at high abundances in the outflows of protostars, its contribution to the chemical evolution of these regions is a minor one due to its limited low temperature reactivity in the gas-phase. Here, we performed kinetic experiments on the barrierless CH + H2O reaction in a supersonic flow reactor down to 50 K. The measured rate increases rapidly below room temperature, confirming and extending the predictions of previous statistical calculations. The open product channels for this reaction suggest that this process could be an important gas-phase route for formaldehyde formation in protostellar envelopes.