Investigation of the rotational spectrum of CH${}_3$${}^{17}$OH and its tentative detection toward Sagittarius B2(N)

Abstract

Methanol is an abundant molecule in space. The column density of CH${}_3^{18}$OH is in some star-forming regions so high that the search for CH${}_3^{17}$OH is promising. But only very few transition frequencies of CH${}_3^{17}$OH with a microwave accuracy have been published thus far. We recorded the rotational spectrum of CH${}_3^{17}$OH between 38 and 1095 GHz employing a methanol sample enriched in ${}^{17}$O 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 CH${}_3^{17}$OH 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). The assignments cover $0\le J\le 45$, $K_a\le 16$, and mainly the $v_t=0$ 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 CH${}_3^{17}$OH along with secure detections of the more abundant isotopologs of methanol toward Sgr B2(N2b). The derived column densities yield isotopic ratios ${}^{12}$C/${}^{13}$C = 25, ${}^{16}$O/${}^{18}$O = 240, and ${}^{18}$O/${}^{17}$O = 3.3, which are consistent with values found earlier for other molecules in Sgr B2. The agreement between the ${}^{18}$O/${}^{17}$O isotopic ratio that we obtained for methanol and the ${}^{18}$O/${}^{17}$O ratios reported in the past for other molecules in Sgr B2(N) strongly supports our tentative interstellar identification of CH${}_3^{17}$OH. The accuracy of the derived line list is sufficient for further radio astronomical searches for this methanol isotopolog toward other star-forming regions.

16 pages, including tables, figures, references and appendices. Abstract slightly shortened. Astronomy and Astrophysics, accepted for publication

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Cited by in corpus (1)

• Reexploring Molecular Complexity with ALMA: Insights into chemical differentiation from the molecular composition of hot cores in Sgr B2(N2)