Co-author paper: Oyama et al

Deuterium fractionation in molecules is known as one of the powerful tools to study chemical processes during star and planet formation. Among various interstellar molecules, methanol often shows very high deuterium fractionation. It is the most abundant saturated organic molecule and is known as a parent species to form more complex organic molecules. However, deriving the abundance of the deuterated methanol suffers from the uncertainty of intrinsic line intensities (Sμ2) of CH3OH isotopologues. Due to their floppy nature, the Sμ2 values are not readily to be theoretically evaluated particularly for the asymmetric-top asymmetric-frame isotopologue such as CH2DOH. In this study, we have measured the line frequencies and their intensities for CH2DOH in the millimeter-wave region from 216 GHz to 264 GHz by using an emission-type millimeter and submillimeter-wave spectrometer. For the a-type transition, derived Sμ2 values are slightly larger than those theoretically reported except for some transitions affected by avoided level crossing. For the b-type transitions, significant systematic differences are found between theoretical and experimental Sμ2 values. The results of the present 29 study enable us to derive CH2DOH abundances from observations accurately, which are 30 essential to understand deuterium fractionation in various sources.