Abstract
The inheritance of material across the star and planet formation process is traced by deuterium fractionation. We report here the first detection of doubly deuterated methanol towards pre-stellar cores. We study the deuterium fractionation of methanol, CH3OH, towards two starless and two pre-stellar cores. We derive a D/H ratio of 0.8–1.9% with CH2DOH in pre-stellar cores H-MM1 and L694-2, consistent with measurements in more evolved Class 0/I objects and comet 67P/Churyumov-Gerasimenko, suggesting a direct chemical link arising in the pre-stellar stage. Furthermore, the column density ratios of CHD2OH/CH2DOH are ∼50–80%, as consistently high as towards Class 0/I objects, indicating an efficient formation mechanism of CHD2OH, possibly through H atom additions to D2CO. The CH2DOH/CH3OH and CHD2OH/CH3OH column density ratios in the two pre-stellar cores are larger than that in the two starless cores B68 and L1521E, representing an evolutionary trend of methanol deuteration in early-stage cores.
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