===== On Methanol, CH3OH, in the ISM ===== Methanol was one of the earliest molecules to be detected by means of radio astronomy. A plethora of reports deserve mentioning here. Therefore, this documentation may well be incomplete for quite a while.\\ J. A. Ball, C. A. Gottlieb, A. E. Lilley, and H. E. Radford\\ gave an account of the\\ **[[https://ui.adsabs.harvard.edu/abs/1970ApJ...162L.203B/abstract|Detection of Methyl Alcohol in Sagittarius]]**\\ //Astrophys. J.// **162**, L203–L210 (1970).\\ They used the 140-foot Greenbank radio telescope for the 110 – 111 transition near 834 MHz to detect methanol in emission from Sagittarius (Sgr) A and B2.\\ \\ C. A. Gottlieb, J. A. Ball, E. W. Gottlieb, and D. F. Dickinson\\ investigated\\ **[[https://ui.adsabs.harvard.edu/abs/1979ApJ...227..422G/abstract|Interstellar Methyl Alcohol]]**\\ //Astrophys. J.// **227**, 422–432 (1979).\\ They used the 11 m Kitt Peak radio telescope to search for the //J// = 2 – 1 transitions of CH3OH, 13CH3OH, and CH3OD in the 3 mm region toward several galactic sources. CH3OH was detected toward 14 sources, at least the majority of these are hot-core sources. The identification of 13CH3OH lines toward Sgr B2 may well be correct (the 12C to 13C ratio of somewhat less than 10 is probably affected by opacity of the CH3OH lines), but the identification of CH3OD toward the same source is definitively incorrect; see for example:\\ A. Belloche, H. S. P. Müller, R. T. Garrod, and K. M. Menten\\ **[[https://doi.org/10.1051/0004-6361/201527268|Exploring Molecular Complexity with ALMA (EMoCA): Deuterated Complex Organic Molecules in Sagittarius B2(N2)]]**\\ //Astron. Astrophys.// **587**, Art. No. A91 (2016).\\ \\ F. F. Gardner, J. B. Whiteoak, J. Reynolds, W. L. Peters, and T. B. H. Kuiper\\ announced the\\ **[[https://doi.org/10.1093/mnras/240.1.35P|First Detection of the 18O Isotope of Methanol]]**\\ //Mon. Not. R. Astron. Soc.// **240**, 35P–40P (1989).\\ The NASA's 70 m dish at Tidbinbilla was used to detect the //JK// = 20 − 3−1 transition of CH318OH near 11.6 GHz toward Sgr B2. The derived 16O to 18O ratio of 210 ± 40 is in line with other results obtained toward the galactic center.\\ \\ R. Mauersberger, C. Henkel, T. Jacq, C. M. Walmsley\\ detected\\ **[[https://ui.adsabs.harvard.edu/abs/1988A%26A...194L...1M/abstract|Deuterated Methanol in Orion]]**\\ //Astron. Astrophys.// **194**, L1−L4 (1988).\\ About one dozen transitions of CH3OD were detected with good signal-to-noise ratios toward Orion KL between 110 and 230 GHz using the IRAM 30 m telescope.\\ \\ T. Jacq, C. M. Walmsley, R. Mauersberger, T. Anderson, E. Herbst, F. C. De Lucia\\ gave an account of the\\ **[[https://ui.adsabs.harvard.edu/abs/1993A%26A...271..276J/abstract|Detection of interstellar CH2DOH]]**\\ //Astron. Astrophys.// **271**, 276–281 (1993).\\ The IRAM 30 m telescope was employed to detect six lines of CH2DOH toward Orion-IRc2 between 90 and 230 GHz. Several CH3OD transitions were observed newly around 136 GHz. The abundance of CH2DOH was estimated to be slightly higher (by up to 50 %) than that of CH3OD.\\ \\ B. Parise, C. Ceccarelli, A. G. G. M. Tielens, E. Herbst, B. Lefloch, E. Caux, A. Castets, I. Mukhopadhyay, L. Pagani, and L. Loinard\\ announced the\\ **[[https://doi.org/10.1051/0004-6361:20021131|Detection of Doubly-deuterated Methanol in the Solar-type Protostar IRAS 16293−2422]]**\\ //Astron. Astrophys.// **393**, L49–L53 (2002).\\ About a dozen lines of CHD2OH were detected between 89 and 224 GHz with very modest to good signal-to-noise ratios employing the IRAM 30 m telescope. The CH2DOH isotopolog has an abundance about five times higher. The comparisons to CH3OH are incorrect because of severe opacity of these lines.\\ \\ In addition,\\ B. Parise, C. Ceccarelli, A. G. G. M. Tielens, A. Castets, E. Caux, B. Lefloch, and S. Maret\\ were\\ **[[https://doi.org/10.1051/0004-6361:20054476|Testing Grain Surface Chemistry: a Survey of Deuterated Formaldehyde and Methanol in Low-mass Class 0 Protostars]]**\\ //Astron. Astrophys.// **453**, 949–958 (2006).\\ CHD2OH was also found toward the low-mass protostars IRAS 2, IRAS 4A, and IRAS 4B in the NGC 1333 molecular cloud.\\ \\ B. Parise, A. Castets, E. Herbst, E. Caux, C. Ceccarelli, I. Mukhopadhyay, and A. G. G. M. Tielens\\ gave an account of the\\ **[[https://doi.org/10.1051/0004-6361:20034490|First Detection of Triply-deuterated Methanol]]**\\ //Astron. Astrophys.// **416**, 159–163 (2004).\\ A dozen lines of CD3OH were detected around 158 GHz toward IRAS 16293−2422 with very modest to reasonable signal-to-noise ratios employing the IRAM 30 m telescope. The column density of CH3OH was derived from that of 13CH3OH. The CH3OH : CH2DOH : CHD2OH : CD3OH ratios were about 126 : 38 : 7.7 : 1.\\ \\ V. V. Ilyushin, H. S. P. Müller, J. K. Jørgensen, S. Bauerecker, C. Maul, R. Porohovoi, E. A. Alekseev, O. Dorovskaya, F. Lewen, S. Schlemmer, and R. M. Lees\\ carried out an\\ **[[https://doi.org/10.1051/0004-6361/202347105|Investigation of the Rotational Spectrum of CD3OD and an Astronomical Search toward IRAS 16293–2422]]**\\ //Astron. Astrophys.// **677**, Art. No. A49 (2023).\\ The authors found some evidence for the presence of this isotopolog in PILS data toward this low-mass protostar. About seven lines are not blended to only partially blended; the signal-to-noise ratio of some lines is only modest. The derived abundance of 0.02 % with respect to the main isotopolog may be reasonable compared to 0.33 % obtained for CD3OH described below. Nevertheless, the identification should be viewed as very tentative because of the limited amount of lines and the complexity found in deueration ratios. Identifications of CH2DOD and also CHD2OD should be more promising.\\ \\ H. S. P. Müller, V. V. Ilyushin, A. Belloche, F. Lewen, and S. Schlemmer\\ reported on an\\ **[[https://doi.org/10.1051/0004-6361/202451011|Investigation of the Rotational Spectrum of CH317OH and its Tentative Detection toward Sagittarius B2(N)]]**\\ //Astron. Astrophys.// **688**, Art. No. A201 (2023).\\ The authors report a tentative detection of this isotopolog in the ReExploring Molecular Complexity with ALMA survey at 3 mm. Only one unblended and one partially blended line were identified, many more were severely bleded or too weak. The derived CH318OH to CH317OH ratio of ~3.3 is along 18O to 17O ratios found for other molecules in the Galactic Center as is the CH316OH to CH318OH ratio of 240.\\ \\ \\ === Vibrationally Excited Methanol === F. J. Lovas, R. D. Suenram, L. E. Snyder, J. M. Hollis, and R. M. Lees\\ reported on the\\ **[[https://ui.adsabs.harvard.edu/abs/1982ApJ...253..149L/abstract|Detection of the Torsionally Excited State of Methanol in Orion A]]**\\ //Astrophys. J.// **253**, 149–153 (1982).\\ Three lines partaining to four transitions of torsionally excited methanol were detected with the 11 m Kitt Peak radio telescope at 3 mm.\\ \\ V. V. Ilyushin, H. S. P. Müller, J. K. Jørgensen, S. Bauerecker, C. Maul, Y. Bakhmat, E. A. Alekseev, O. Dorovskaya, S. Vlasenko, F. Lewen, S. Schlemmer, K. Berezkin, and R. M. Lees\\ investigated the\\ **[[https://doi.org/10.1051/0004-6361/202142326|Rotational and Rovibrational Spectroscopy of CD3OH with an Account of CD3OH toward IRAS 16293−2422]]**\\ //Astron. Astrophys.// **658**, Art. No. A127 (2022).\\ Using the Protostellar Interferometric Line Survey (PILS) carried out with ALMA, several lines of torsionally excited CD3OH were detected between 329 and 363 GHz; nine unblended or only slightly blended lines of this vibrationally excited state were shown in a figure around 350.6 GHz. The rotational temperature was ~225 K, and the CH3OH to CD3OH ratio was about 300. Lines of torsionally excited deuterated methanol will be more prominent for 12C isotopologs containing fewer D atoms.\\ \\ 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, L.-H. Xu, and R. M. Lees reported on the\\ **[[https://doi.org/10.1051/0004-6361/202449918|Rotational Spectroscopy of CH3OD with a reanalysis of CH3OD toward IRAS 16293–2422]]**\\ //Astron. Astrophys.// **687**, Art. No. A220 (2024).\\ Unsurprisingly, the authors detected in their PILS data also many lines of CH3OD in //v//t = 1. These lines were instrumental in determing the rotational temperature of ~190 K, which is in accord with ~225 K mentioned in the previous paragraph, but considerably lower than the estimated ~300 K earlier. Adopting earlier values, the amount of CH3OD is ~0.32 % that of CH3OH, and the CH2DOH to CH3OD ratio is ~22.5, which translates into a deuteration ratio per H atom of ~7.5.\\ \\ H. S. P. Müller, V. V. Ilyushin, A. Belloche, F. Lewen, and S. Schlemmer\\ reported on an\\ **[[https://doi.org/10.1051/0004-6361/202451011|Investigation of the Rotational Spectrum of CH317OH and its Tentative Detection toward Sagittarius B2(N)]]**\\ //Astron. Astrophys.// **688**, Art. No. A201 (2023).\\ The authors report a tentative detection of torsionally excited CH318OH in the ReExploring Molecular Complexity with ALMA survey at 3 mm besides several a clear identification of this isotopolog in its ground torsional state.\\ \\ ---- Contributor(s): H. S. P. Müller; 04, 2022; 08, 2024 ----