The millimeter-wave rotational transition line (JK = 1 0-00) of deuterated methane CH3D has tentatively been detected toward the low-mass Class 0 protostar IRAS 04368+2557 in L1527 with the Heinrich Hertz Submillimeter Telescope. This is the first detection of CH3D in interstellar clouds, if confirmed. The column density and fractional abundance of CH3D are determined to be (9.1 ± 3.4) × 1015cm-2 and (3.0 ± 1.1) × 10-7, respectively, where we assume the rotational temperature of 25K. The column density and fractional abundance of the gaseous CH4 are estimated to be (1.3-4.6) × 1017cm -2 and (4.3-15.2) × 10-6, respectively, by adopting the molecular D/H ratios of 2%-7% reported for various molecules in L1527. The fractional abundance of CH4 is higher than or comparable to that found in high-mass star-forming cores by infrared observations. It is sufficiently high to trigger the efficient production of various carbon-chain molecules in a lukewarm region near the protostar, which supports the scenario of warm carbon-chain chemistry.
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