Astrochemistry

Rotational Spectroscopy of CH3OD with a Reanalysis of CH3OD Toward IRAS 16293−2422

By Keith Cowing

Status Report

astro-ph.GA

July 13, 2024

Filed under ALMA, astro-ph.GA, astrochemistry, astronomy, biochemistry, Interstellar, IRAS 16293--2422, Methanol, methanol isotopolog, organic chemistry, prestellar core, Spectroscopy

Rotational Spectroscopy of CH3OD with a Reanalysis of CH3OD Toward IRAS 16293−2422 — Comparison between the observed PILS spectrum and the synthetic spectra obtained using the (old) spectroscopic data utilized in Jørgensen et al. (2018) (in blue) and the current spectroscopy (in red). The two synthetic spectra at an offset of 0.6 Jy beam−1 correspond to the prediction from the fit of the 2018 paper (solid blue curve) and current spectroscopy (dashed red curve), adopting the excitation temperature of 300 K from Jørgensen et al. (2018) and the column density from that same paper corrected for the factor of four error discussed in Section 5 (N = 4.5 × 1016 cm−2 ). These two synthetic spectra are virtually identical except for two high excitation transitions at 362.7685 and 362.8805 GHz, where the new spectroscopic model demonstrates one clearly overpredicted transition (marked by an arrow). The synthetic spectrum at an offset of 0 Jy/beam correspond to the prediction with the lower inferred excitation temperature from the analysis summarized in Table 2, shown with a red curve. As can be seen, this spectrum matches well the high excitation 362.7685 and 362.8805 GHz transitions, which were not included in the old spectroscopy. These two lines come out at appropriate intensities in comparison to the observations within the uncertainties of the model. — astro-ph.GA

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. 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 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 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.

V. V. Ilyushin, H. S. P. Müller, M. N. Drozdovskaya, J. K. Jørgensen, S. Bauerecker, C. Maul, R. Porohovoi, E. A. Alekseev, O. Dorovskaya, O. Zakharenko, F. Lewen, S. Schlemmer, R. M. Lees

Comments: 12 pages including figures, tables, references and appendix. Astron. Astrophys., in press
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2406.08236 [astro-ph.GA] (or arXiv:2406.08236v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2406.08236
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Related DOI:
https://doi.org/10.1051/0004-6361/202449918
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Submission history
From: Holger Müller
[v1] Wed, 12 Jun 2024 14:02:12 UTC (491 KB)
https://arxiv.org/abs/2406.08236
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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