2022ApJ...932..101O

Methanol (CH₃OH) is an abundant interstellar species and is known to be an important precursor of various interstellar complex organic molecules. Among the methanol isotopologues, CH₂DOH is one of the most abundant isotopologues and it is often used to study the deuterium fractionation of CH₃OH in interstellar medium. However, the emission lines of CH₂DOH can sometimes be optically thick, making the derivation of its abundance unreliable. Therefore, observations of its presumably optically thin ¹³C substituted species, ¹³CH₂DOH, are essential to overcome this issue. In this study, the rotational transitions of ¹³CH₂DOH have been measured in the millimeter-wave region from 216 GHz to 264 GHz with an emission-type millimeter- and submillimeter-wave spectrometer by using a deuterium and ¹³C enriched sample. The frequency accuracy of measured ¹³CH₂DOH is less than a few kHz, and the relative line intensity error is less than 10% in most of the frequency range by taking advantage of the wide simultaneous frequency-coverage of the emission-type spectrometer. These results offer a good opportunity to detect ¹³CH₂DOH in space, which will allow us to study the deuterium fractionation of CH₃OH in various sources through accurate determination of the CH₂DOH abundance.