| Summary: | We have observed the ^13 CH _3 OH 5 _1 −4 _1 A ^+ , ^13 CH _3 OH 14 _1 −13 _2 A ^− , and CH _2 DOH 8 _2,6 −8 _1,7 e _0 lines toward 24 high-mass star-forming regions by using Atacama Large Millimeter/submillimeter Array with an angular resolution of about 0 $\mathop{.}\limits^{\unicode{x02033}}$ 3. This resolution corresponds to a linear scale of 400–1600 au, allowing us to resolve individual cores properly. We detected the ^13 CH _3 OH and CH _2 DOH emission near the continuum peaks in many of these regions. From the two ^13 CH _3 OH lines, we calculated the temperature toward the ^13 CH _3 OH peaks, and confirm that the emission traces hot (>100 K) regions. The N(CH _2 DOH)/N( ^12 CH _3 OH) ratio in the observed high-mass star-forming regions is found to be lower than that in low-mass star-forming regions. We have found no correlation between the N(CH _2 DOH)/N( ^13 CH _3 OH) or N(CH _2 DOH)/N( ^12 CH _3 OH) ratios and either temperatures or distance to the sources, and have also found a source-to-source variation in these ratios. Our model calculations predict that the N(CH _2 DOH)/N( ^12 CH _3 OH) ratio in hot cores depends on the duration of the cold phase; the shorter the cold phase, the lower the deuterium fractionation in the hot cores. We have suggested that the lower N(CH _2 DOH)/N( ^12 CH _3 OH) ratio in high-mass star-forming regions compared to that in low-mass star-forming regions is due to the shorter duration of the cold phase and that the diversity in the N(CH _2 DOH)/N( ^12 CH _3 OH) ratio in high-mass star-forming regions is due to the diversity in the length of the cold prestellar phase, and not the time that the objects have been in the hot core phase.
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