THE DETECTION OF HOT ETHANOL IN G34.3+0.15

Hot molecular cores in star-forming regions are known to have gas-phas e chemical compositions determined by the evaporation of material from the icy mantles of interstellar grains, followed by subsequent reacti ons in the gas phase. Current models suggest that the evaporated mater ial is rich in hydrogenated species, such as water, methane and methan ol. In this paper, we report the detection of 14 rotational transition s of ethanol in the submillimetre spectrum of the molecular cloud asso ciated with the ultra-compact H II region G34.3+0.15. We derive a rota tion temperature of 125 K and a beam-averaged column density of 2.0x10 (15) cm(-2), corresponding to a fractional abundance on the order of 4 x10(-9). This large abundance, which is a lower limit due to the likel ihood of beam dilution, cannot be made by purely gas-phase processes, and we conclude that the ethanol must be formed efficiently in the gra in surface chemistry. Since it has been argued previously that methano l is formed via surface chemistry, it appears that alcohol formation m ay be a natural by-product of surface reactions.