Rotational spectroscopy of CH3OD with a re-analysis of CH3OD toward IRAS 16293 - 2422

Supplementary material for the article 'Rotational spectroscopy of CH3OD with a re-analysis of CH3OD toward IRAS 16293 - 2422' by V.V. Ilyushin, H.S.P. Muller, M.N. Drozdovskaya, J.K. Jorgensen, S. Bauerecker, C. Maul, R. Porohovoi, E.A. Alekseev, O. Dorovskaya, O. Zakharenko, F. Lewen, S. Schlemmer, L.-H. Xu, and R.M. Lees accepted for publication by Astronomy and Astrophysics.

ADC_Keywords: Interstellar medium; Spectra, millimetric/submm; Spectroscopy

Keywords: Molecular data - Methods: laboratory: molecular - Techniques: spectroscopic - ISM: molecules - Astrochemistry - ISM: individual objects: IRAS 16293 - 2422

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 vibration-torsion-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. Deuteration, in turn, is frequently viewed as a diagnostic tool for star formation. The present measurements were obtained in two spectroscopic laboratories and cover large fractions of the 34 GHz-1.35 THz range. We employed a torsion-rotation Hamiltonian model for our analysis that is based on the rho-axis method as in previous studies. The resulting model describes the ground and first excited torsional states of CH3OD well up to quantum numbers J = 51 and Ka = 18. We derived a line list for radio-astronomicalobservations 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 (PILS) of IRAS 16293-2422 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). 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.

Description:Table C1 contains assigned microwave transitions of the CH3OD spectrum usedin the analysis. Source of data: Khar  - Kharkov spectrometer, present work;Koln - Cologne spectrometers, present work; for other source codes (B, C, D, E, L, T, W) see Duan, Y. B., Ozier, I., Tsunekawa, S., & Takagi, K. 2003, J. Mol. Spectrosc., 218, 95

Table C2 contains assigned FIR transitions of the CH3OD spectrum used inthe analysis. Source of data: Mukhopadhyay, I. 2021, Infrared Phys. Technol., 116, 103605.

Table C3 contains predicted transitions of the ground and first excited torsional states of CH3OD in the frequency range from 1 GHz up to 2 THz with J up to 55 and |Ka| up to 21. The m values 0/1 and -3/-2 correspond to A/E transitions of the vt = 0 and 1 torsional states, respectively. We limit our calculations to transitions for which uncertainties are less than 0.1 MHz.

Table C4 contains torsion-rotation part Qrt(T) of the total internal partition function Q(T)=Qv(T)*Qrt(T), calculated for CH3OD from first principles using the parameter set of Table A.1. In the calculation the states up to J=65 and vt=11 were included. The vibrational part Qv(T) (omitting the torsional vibration since it is taken into account in Qrt) may be estimated in the harmonic approximation using the vibrational frequencies reported by T. Schimanouchi, Tables of Molecular Vibrational Frequencies, Vol. I: consolidated (National Bureau of Standards, Washington, DC, 1972), pp. 1-160. 

File Summary:-----------------------------------------------------------------------------------------------------------------------  FileName   Lrecl  Records   Explanations-----------------------------------------------------------------------------------------------------------------------readme.txt      80       tablec1.dat     75    11118   Assigned microwave transitions of the CH3OD                                                       spectrum used in the analysis. tablec2.dat     71     5465    Assigned FIR transitions of the CH3OD spectrum                                                      used in the analysis. tablec3.dat     87    25111   Predicted transition frequencies of the ground and                                                     first excited torsional states of CH3OD in the                                                     frequency range from 1 GHz up to 2 THz.tablec4.dat     16       30     Torsion-rotation part Qrt(T) of the total internal                                                    partition function Q(T)=Qv(T)*Qrt(T), calculated                                                    for CH3OD from first principles.------------------------------------------------------------------------------------------------------------------------