  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. Whilst water vapour 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
earlier 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.
