J/A+A/vol/page Spectroscopy of CH3^17OH (Muller+, 2024) ================================================================================ Investigation of the rotational spectrum of CH3^17OH and its tentative detection toward Sagittarius B2(N) H.S.P. Muller, V.V. Ilyushin, A. Belloche, F. Lewen, and S. Schlemmer =2024A&A...VVV.ppppI (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: Context. Methanol is an abundant and widespread molecule in the interstellar medium. The abundance of its 18O isotopolog, CH3^18OH, is in some star forming regions so high that the search for CH3^17OH is promising. But only very few transition frequencies of CH3^17OH with microwave accuracy have been published prior to our investigation. Aims. We want to extend the very limited rotational line list of CH3^17$OH to be able to search for this isotopolog in the interstellar medium. Methods. We recorded the rotational spectrum of CH3^17OH between 38 and 1095 GHz employing a methanol sample enriched in 17O to 20%. A torsion-rotation Hamiltonian model based on the rho-axis method was employed to fit the data, as in our previous studies. We searched for rotational transitions of CH3^17OH in the imaging spectral line survey ReMoCA obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star forming region Sgr B2(N). The observed spectra were modeled under the assumption of local thermodynamic equilibrium (LTE). Results. The assignments cover 0 <= J <= 45, Ka <= 16, and mainly the vt = 0 and 1 torsional states. The Hamiltonian model describes our data well. The model was applied to derive a line list for radio-astronomical observations. We report a tentative detection of CH3^17OH along with secure detections of the more abundant isotopologs of methanol toward Sgr B2(N2b). The derived column densities yield isotopic ratios 12C/13C = 25, 16O/18O = 240, and 18O/17O = 3.3, which are consistent with values found earlier for other molecules in Sgr B2. Conclusions. The agreement between the 18O/17O isotopic ratio that we obtained for methanol and the 18O/17O ratios reported in the past for other molecules in Sgr B2(N) strongly supports our tentative interstellar identification of CH3^17OH. The accuracy of the derived line list is sufficient for further radio astronomical searches for this methanol isotopolog toward other star forming regions. Description: Table C1 contains assigned microwave transitions of the CH3^17OH spectrum used in the analysis. Source of data: Koln - Cologne spectrometers, present work; UT91 - Hoshino, Y., Ohishi, M., & Takagi, K. 1991, J. Mol. Spectrosc., 148, 506. The intensity-weighted average was used if two or more transition frequencies are the same. Table C2 contains assigned FIR transitions of the CH3^17OH spectrum used in the analysis. Source of data: Moruzzi, G., Murphy, R. J., Vos, J., et al. 2011, J. Mol. Spectrosc., 268, 211. The intensity-weighted average was used if two or more transition frequencies are the same. Table C3 contains predicted transitions of the ground and first excited torsional states of CH3^17OH in the frequency range from 1 GHz up to 1.1 THz with J up to 50 and |Ka| up to 17. The m values 0/1 correspond to A/E transitions, respectively, of the vt = 0 torsional state, those with -2/-3 to A/E transitions, respectively, of the vt = 1 torsional state. We limit our calculations to transitions for which uncertainties are less than 0.1 MHz. The file does not consider hyperfine splitting of the 17O nuclues. Table C4 contains predicted transitions of the ground and first excited torsional states of CH3^17OH in the frequency range from 1 GHz up to 1.1 THz with J up to 50 and |Ka| up to 17. The m values 0/1 correspond to A/E transitions, respectively, of the vt = 0 torsional state, those with -2/-3 to A/E transitions, respectively, of the vt = 1 torsional state. We limit our calculations to transitions for which uncertainties are less than 0.1 MHz. The file does consider hyperfine splitting of the 17O nuclues. Table C5 contains torsion-rotation part Qrt(T) of the total internal partition function Q(T)=Qv(T)*Qrt(T), calculated for CH3^17OH 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. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe.txt 80 . This file TableC1.dat 87 4790 Assigned microwave transitions of the CH3^17OH spectrum used in the analysis. TableC2.dat 70 7851 Assigned FIR transitions of the CH3^17OH spectrum used in the analysis. TableC3.dat 87 9993 Predicted hypothetical hyperfine free torsion- rotation transition frequencies of the ground and first excited torsional states of CH3^17OH in the frequency range from 1 GHz up to 1.1 THz. TableC4.dat 99 102317 Predicted transition frequencies of the ground and first excited torsional states of CH3^17OH taking into account quadrupole hyperfine splitting in the frequency range from 1 GHz up to 1.1 THz. TableC5.dat 16 30 Torsion-rotation part Qrt(T) of the total internal partition function Q(T)=Qv(T)*Qrt(T), calculated for CH3^17OH 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- 11 F5.1 --- F' Upper F quantum number (F' = -1.0 for hypothetical hyperfine free transition) 13- 15 I3 --- J' Upper J quantum number 17- 19 I3 --- Ka' Upper Ka quantum number 21- 23 I3 --- Kc' Upper Kc quantum number 28- 29 A2 --- Sym" Lower level symmetry in the G6 group 31- 32 I2 --- m" Lower free rotor torsional quantum number 34- 38 F5.1 --- F" Lower F quantum number (F" = -1.0 for hypothetical hyperfine free transition) 40- 42 I3 --- J" Lower J quantum number 44- 46 I3 --- Ka" Lower Ka quantum number 48- 50 I3 --- Kc" Lower Kc quantum number 53- 64 F12.4 MHz Freq Observed transition frequency 66- 71 F6.3 MHz unc Uncertainty of measurement 73- 80 F8.4 MHz O-C Residuals from the fit 84- 87 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- 49 F11.4 cm-1 Freq Observed transition frequency 53- 59 F7.4 cm-1 unc Uncertainty of measurement 63- 70 F9.4 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- 2 A2 --- Sym' Upper level symmetry in the G6 group 4- 5 I2 --- m' Upper free rotor torsional quantum number 7- 11 F5.1 --- F' Upper F quantum number 13- 15 I3 --- J' Upper J quantum number 17- 19 I3 --- Ka' Upper Ka quantum number 21- 23 I3 --- Kc' Upper Kc quantum number 28- 29 A2 --- Sym" Lower level symmetry in the G6 group 31- 32 I2 --- m" Lower free rotor torsional quantum number 34- 38 F5.1 --- F" Lower F quantum number 40- 42 I3 --- J" Lower J quantum number 44- 46 I3 --- Ka" Lower Ka quantum number 48- 50 I3 --- Kc" Lower Kc quantum number 52- 64 F13.4 MHz Freq Predicted transition frequency 67- 74 F8.4 MHz unc Predicted uncertainty of transition frequency 78- 87 F10.4 cm-1 Elo The energy of the lower state 90- 99 E10.3 D^2 Sm2 Dipole moment squared multiplied by the transition linestrength -------------------------------------------------------------------------------- Byte-by-byte Description of file: TableC5.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) Holger Muller [Koln University] 04-Jun-2024