Spectroscopy of CH3OD                      (Ilyushin+, 2024)
================================================================================
Rotational spectroscopy of CH3OD with a re-analysis of CH3OD 
toward IRAS 16293 - 2422

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
================================================================================
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-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 (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 used
in 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 in
the 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        .   This file
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.
--------------------------------------------------------------------------------


Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  2 A2     ---    Sym'  Upper level symmetry in the G6 group
   4-  5 I2     ---    m'    Upper free rotor torsional quantum number
   7-  9 I3     ---    J'    Upper J quantum number
  11- 13 I3     ---    Ka'   Upper Ka quantum number
  15- 17 I3     ---    Kc'   Upper Kc quantum number
  22- 23 A2     ---    Sym"  Lower level symmetry in the G6 group
  25- 26 I2     ---    m"    Lower free rotor torsional quantum number
  28- 30 I3     ---    J"    Lower J quantum number
  32- 34 I3     ---    Ka"   Lower Ka quantum number
  36- 38 I3     ---    Kc"   Lower Kc quantum number
  40- 51 F12.3  MHz    Freq  Observed transition frequency
  54- 59 F6.3   MHz    unc   Uncertainty of measurement
  62- 69 F8.4   MHz    O-C   Residuals from the fit
  72- 75 A4     ---    Cmnt  Source of data
--------------------------------------------------------------------------------


Byte-by-byte Description of file: tablec2.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  2 A2     ---    Sym'  Upper level symmetry in the G6 group
   4-  5 I2     ---    m'    Upper free rotor torsional quantum number
   7-  9 I3     ---    J'    Upper J quantum number
  11- 13 I3     ---    Ka'   Upper Ka quantum number
  15- 17 I3     ---    Kc'   Upper Kc quantum number
  22- 23 A2     ---    Sym"  Lower level symmetry in the G6 group
  25- 26 I2     ---    m"    Lower free rotor torsional quantum number
  28- 30 I3     ---    J"    Lower J quantum number
  32- 34 I3     ---    Ka"   Lower Ka quantum number
  36- 38 I3     ---    Kc"   Lower Kc quantum number
  40- 50 F11.5  cm-1   Freq  Observed transition frequency
  53- 59 F7.4   cm-1   unc   Uncertainty of measurement
  63- 71 F9.5   cm-1   O-C   Residuals from the fit
--------------------------------------------------------------------------------


Byte-by-byte Description of file: tablec3.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  2 A2     ---    Sym'  Upper level symmetry in the G6 group
   4-  5 I2     ---    m'    Upper free rotor torsional quantum number
   7-  9 I3     ---    J'    Upper J quantum number
  11- 13 I3     ---    Ka'   Upper Ka quantum number
  15- 17 I3     ---    Kc'   Upper Kc quantum number
  22- 23 A2     ---    Sym"  Lower level symmetry in the G6 group
  25- 26 I2     ---    m"    Lower free rotor torsional quantum number
  28- 30 I3     ---    J"    Lower J quantum number
  32- 34 I3     ---    Ka"   Lower Ka quantum number
  36- 38 I3     ---    Kc"   Lower Kc quantum number
  40- 52 F13.4  MHz    Freq  Predicted transition frequency
  55- 62 F8.4   MHz    unc   Predicted uncertainty of transition frequency
  66- 75 F10.4  cm-1   Elo   The energy of the lower state
  78- 87 E10.3  D^2    Sm2   Dipole moment squared multiplied by the transition 
                                linestrength
--------------------------------------------------------------------------------


Byte-by-byte Description of file: tablec4.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  5 F5.1   K       T    Temperature 
   8- 16 F9.2   ---     Qrt  Torsion-rotation part of the partition function
--------------------------------------------------------------------------------

================================================================================
(End)          Vadim Ilyushin [IRA NASU]                      08-Mar-2024