First detection of CHD$_{2}$OH towards pre-stellar cores

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, CH$_{3}$OH, towards two starless and two pre-stellar cores. We derive a D/H ratio of 0.8-1.9$\%$ with CH$_{2}$DOH 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 CHD$_{2}$OH/CH$_{2}$DOH are $\sim$50-80$\%$, consistently high as that towards Class 0/I objects, indicating an efficient formation mechanism of CHD$_{2}$OH, possibly through H atom additions to D$_{2}$CO. The CH$_{2}$DOH/CH$_{3}$OH and CHD$_{2}$OH/CH$_{3}$OH 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.