Investigation of the rotational spectrum of CH_3^17OH and its tentative detection toward Sagittarius B2(N)
arxiv(2024)
Abstract
Methanol is an abundant molecule in space. The column density of
CH_3^18OH is in some star-forming regions so high that the search for
CH_3^17OH is promising. But only very few transition frequencies of
CH_3^17OH with a microwave accuracy have been published thus far. We
recorded the rotational spectrum of CH_3^17OH 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
CH_3^17OH 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). The assignments cover 0
≤ J ≤ 45, K_a ≤ 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_3^17OH 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. 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 CH_3^17OH. The accuracy of the derived line
list is sufficient for further radio astronomical searches for this methanol
isotopolog toward other star-forming regions.
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