Rotational spectroscopy of CH₃OD with a reanalysis of CH₃OD toward IRAS 16293–2422^*

¹ Institute of Radio Astronomy of NASU, Mystetstv 4, 61002 Kharkiv, Ukraine
e-mail: ilyushin@rian.kharkov.ua
² Astrophysik/I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: hspm@ph1.uni-koeln.de
³ Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD/WRC), Dorfstrasse 33, 7260, Davos Dorf, Switzerland
⁴ Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark
⁵ Institut für Physikalische und Theoretische Chemie, Technische Universität Braunschweig, Gaußstr. 17, 38106 Braunschweig, Germany
⁶ Univ. Lille, CNRS, UMR 8523 – PhLAM – Physique des Lasers Atomes et Molécules, 59000 Lille, France
⁷ Department of Physics, University of New Brunswick, Saint John, NB E2L 4L5, Canada

Received: 9 March 2024
Accepted: 27 May 2024

Abstract

We have started a measurement campaign of numerous methanol isotopologs in low-lying torsional states in order to provide extensive line lists for radio astronomical observations from an adequate spectroscopic model and to investigate how the intricate vibrationtorsion-rotation interactions manifest themselves in the spectra of different isotopic species. After CD₃OH and CD₃OD, we turn our focus to CH₃OD, which is an important species for studying deuteration in prestellar cores and envelopes that enshroud protostars. Notably, deuteration is frequently viewed as a diagnostic tool for star formation. The measurements used in this study were obtained in two spectroscopic laboratories and cover large fractions of the 34 GHz-1.35 THz range. As done in previous studies, we employed a torsion-rotation Hamiltonian model for our analysis that is based on the rho-axis method. The resulting model describes the ground and first excited torsional states of CH₃OD well up to quantum numbers J ⩽ 51 and K_a ⩽ 18. We derived a line list for radio astronomical observations from this model that is accurate up to at least 1.35 THz and should be sufficient for all types of radio astronomical searches for this methanol isotopolog in these two lowest torsional states. This line list was applied to a reinvestigation of CH₃OD in data from the Protostellar Interferometric Line Survey of IRAS 16293–2422 obtained with the Atacama Large Millimeter/submillimeter Array. The new accurately determined value for the column density of CH₃OD implies that the deuteration in methanol differs in its two functional groups by a factor of ~7.5.