J/A+A/677/A49 Spectroscopy of CD3OD (Ilyushin+, 2023) ================================================================================ Investigation of the rotational spectrum of CD_3_OD and an astronomical search for it toward IRAS 16293-2422. Ilyushin V.V., Muller H.S.P., Jorgensen J.K., Bauerecker S., Maul C., Porohovoi R., Alekseev E.A., Dorovskaya O., Lewen F., Schlemmer S., Lees R.M. =2023A&A...677A..49I (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Interstellar medium ; Spectra, millimetric/submm; Spectroscopy Keywords: molecular data - methods: laboratory: molecular - techniques: spectroscopic - radio lines: ISM - ISM: molecules - astrochemistry Abstract: Solar-type prestellar cores and protostars display frequently large amounts of deuterated organic molecules and in particular high relative abundances of doubly and triply deuterated isotopologs. Recent findings on CHD_2_OH and CD_3_OH toward IRAS 16293-2422 suggest that even fully deuterated methanol, CD_3_OD, may be detectable as well. However, searches for CD_3_OD are hampered in particular by the lack of intensity information from a spectroscopic model. The objective of the present investigation is to develop a spectroscopic model of CD_3_OD in low-lying torsional states that is sufficiently accurate to facilitate searches for this isotopolog in space. We carried out a new measurement campaign for CD_3_OD involving two spectroscopic laboratories that covers the 34 GHz-1.1THz range. A torsion-rotation Hamiltonian model based on the rho-axis method was employed for our analysis. Our resulting model describes the ground and first excited torsional states of CD_3_OD well up to quantum numbers J<=51 and Ka<=23. We derived a line list for radio-astronomical observations from this model that is accurate up to at least 1.1THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. This line list was used to search for CD_3_OD in data from the Protostellar Interferometric Line Survey of IRAS 16293-2422 obtained with the Atacama Large Millimeter/ submillimeter Array. While we found several emission features that can be attributed largely to CD_3_OD, their number is as yet insufficient to establish a clear detection. Nevertheless, the estimate of 2x10^15cm^-2^ derived for the CD3OD column density may be viewed as an upper limit that can be compared to column densities of CD_3_OH, CH_3_OD, and CH_3_OH. The comparison indicates that the CD_3_OD column density toward IRAS 16293-2422 is in line with the enhanced D/H ratios observed for multiply deuterated complex organic molecules. Description: Table B1 contains assigned microwave transitions of the CD_3_OD spectrum used in the analysis. Source of data: Khark - Kharkov spectrometer, present work; Koln - Cologne spectrometers, present work; for other source codes (A,C,D,E,F) see H.S.P. Muller, L.-H. Xu, & F. van der Tak 2006, J. Mol. Struct., 795, 114. Table B2 contains assigned FIR transitions of the CD_3_OD spectrum used in the analysis. Source of data: I. Mukhopadhyay, Infrared Physics & Technology 114 (2021) 103668. Table B3 contains predicted transitions of the ground and first excited torsional states of CD_3_OD in the frequency range from 1GHz up to 1.33THz with J up to 55 and |Ka| up to 25. 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 B4 contains torsion-rotation part Qrt(T) of the total internal partition function Q(T)=Qv(T)*Qrt(T), calculated for CD3OD from first principles using the parameter set of Table A.1. 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. In the calculation the states up to J=90 and vt=11 were included. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tableb1.dat 76 11232 Assigned microwave transitions of the CD_3_OD spectrum used in the analysis tableb2.dat 71 5027 Assigned FIR transitions of the CD_3_OD spectrum used in the analysis tableb3.dat 87 32334 Predicted transition frequencies of the ground and first excited torsional states of CD_3_OD in the frequency range from 1GHz up to 1.33THz tableb4.dat 16 30 Torsion-rotation part Qrt(T) of the total internal partition function Q(T)=Qv(T)*Qrt(T), calculated for CD3OD from first principles -------------------------------------------------------------------------------- Byte-by-byte Description of file: tableb1.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- 76 A5 --- Cmnt Source of data (1) -------------------------------------------------------------------------------- Note (1): Source of data as follows: Khark = Kharkov spectrometer, present work Koln = Cologne spectrometers, present work A = see Muller, Xu, & van der Tak 2006, J. Mol. Struct., 795, 114 C = see Muller, Xu, & van der Tak 2006, J. Mol. Struct., 795, 114 D = see Muller, Xu, & van der Tak 2006, J. Mol. Struct., 795, 114 E = see Muller, Xu, & van der Tak 2006, J. Mol. Struct., 795, 114 F = see Muller, Xu, & van der Tak 2006, J. Mol. Struct., 795, 114 -------------------------------------------------------------------------------- Byte-by-byte Description of file: tableb2.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: tableb3.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 D2 Sm2 Dipole moment squared multiplied by the transition linestrength and nuclear spin statistical weight -------------------------------------------------------------------------------- Byte-by-byte Description of file: tableb4.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 -------------------------------------------------------------------------------- Acknowledgements: Vadim Ilyushin, ilyushin(at)rian.kharkov.ua ================================================================================ (End) Vadim Ilyushin [IRA NASU], Patricia Vannier [CDS] 02-Jul-2023