Discovery of the methoxy radical, CH_ 3O, toward B1: Dust grain and gas-phase chemistry in cold dark clouds

摘要

We report on the discovery of the methoxy radical (CH_ 3O) toward the cold and dense core B1-b based on the observation, with the IRAM 30m radio telescope, of several lines at 3 and 2mm wavelengths. Besides this new molecular species we also report on the detection of many lines arising from methyl mercaptan (CH_ 3SH), formic acid (HCOOH), propynal (HCCCHO), acetaldehyde (CH_ 3CHO), dimethyl ether (CH_ 3OCH_ 3), methyl formate (CH_ 3OCOH), and the formyl radical (HCO). The column density of all these species is ?10~ (12) cm~ (-2), corresponding to abundances of ?10~ (-11). The similarity in abundances for all these species strongly suggest that they are formed on the surface of dust grains and ejected to the gas phase through non-thermal desorption processes, most likely cosmic rays or secondary photons. Nevertheless, laboratory experiments indicate that the CH_ 3O isomer released to the gas phase is CH_ 2OH rather than the methoxy one. Possible gas-phase formation routes to CH_ 3O from OH and methanol are discussed.