2025ApJ...980..110T

Methanol is one of the most abundant complex organic molecules in interstellar environments. Molecular lines of its rare isotopologues ¹²CH₃¹⁷OH and ¹²CH₃¹⁸OH therefore play a crucial role in examining the column density of ¹²CH₃¹⁶OH, which serves as a reference for organic molecular chemistry in interstellar clouds. In this study, we have recorded the spectroscopic emission spectrum of ¹²CH₃¹⁷OH in the frequency range between 216 and 264 GHz by making use of an emission-type millimeter and submillimeter spectrometer. We have specifically paid attention to the Q-branch transitions, which are the strongest line series in this frequency region. Among the stable oxygen isotopes, ¹⁶O, ¹⁷O, and ¹⁸O of methanol, only ¹²CH₃¹⁷OH obviously shows line profiles having double and/or triple peaks in low-J transitions, due to the nuclear quadrupole interaction. The newly obtained ¹²CH₃¹⁷OH data will play an important role in facilitating a deeper understanding of the organic chemistry related to star and planet formation. The ¹²CH₃¹⁷OH line data allow us to trace and constrain the isotopic ratio ¹⁷O/¹⁸O in methanol, which is efficient to investigate the galactic-scale evolution of elements. In addition, we also assigned some transitions of ¹³CH₃¹⁷OH in the recorded spectrum.