We have observed emission from both ortho and para spin states of ketene (CH2CO) towards several deeply-embedded protostars. The low CH 2CO fractional abundances (∼10-10) and the rotation temperatures (∼20 K) are consistent with emission from the cooler envelope. We compare our results with previous studies and discuss possible production pathways to interstellar ketene. We suggest that, if low observed excitation temperatures of CH2CO, CH3CHO and H2CO are indicative of their absence from the hot core region, then this may be due to the extensive hydrogenation of pre-existing grain mantles prior to evaporation into the inner envelope, leading to lower abundances of these compounds and to mantles rich in alcohols.
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