molecules:ism:proh [CDMS classic documentation]

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===== Propanol Isomers, C3H7OH, in Space =====

There are two isomers of propanol, the straight-chain //normal//- or just //n//-propanol, also known as 1-propanol, and the branched //iso//- or just //i//-propanol, also known as 2-propanol. There is another structural isomer, **[[molecules:ism:eme|ethyl methyl ether]]**, also known as methoxyethane (CH<sub>3</sub>OC<sub>2</sub>H<sub>5</sub>), whose detection was already reported.\\

To make matters more complicated, //n//-propanol exists in five conformers which are descrobed by the orientation of the terminal CH<sub>3</sub> group and by the OH group. The //anti// conformation refers to a dihedral angle of 180<sup>o</sup> with respect to the CCO plane, whereas the  //gauche// conformations refer to a dihedral angle of ±60<sup>o</sup>. //A// and //G// refer to the orientations of the methyl group, //a//, //g//, and //g'// to that of the OH group. //Ga// is the lowest energy conformer, //Gg// and //Gg'// are higher in energy, and the energy differences are known very well from rotational spectroscopy. //Aa// is probably between //Ga// and //Gg// while //Ag// may be highest in energy. Tunneling within //Ag// leads to //Ag//<sup>+</sup> and //Ag//<sup>−</sup> substates which are separated in energy by roughly 100 GHz.\\

2-Propanol occurs in two conformers //a// and //g//, respectively, with //a// about 85 cm<sup>−1</sup> higher in energy. Tunneling within //g// leads to //g//<sup>+</sup> and //g//<sup>−</sup> substates which are separated in energy by 46.8 GHz.\\
\\

I. Jimenez-Serra, L. F. Rodríguez-Almeida, J. Martín-Pintado, V. M. Rivilla, M. Melosso, S. Zeng, L. Colzi, Y. Kawashima, E. Hirota, C. Puzzarini, B. Tercero, P. de Vicente, F. Rico-Villas, M. A. Requena-Torres, and S. Martín\\
reported on\\
**[[https://doi.org/10.1051/0004-6361/202142699|Precursors of Fatty Alcohols in the ISM: Discovery of //n//-Propanol]]**\\
//Astron. Astrophys.// **663** (2022), Art. No. A181.\\
Transitions of the //Ga// and //Aa// conformers of 1-propanol were observed in the course of molecular line surveys of the quiescent giant molecular cloud G+0.693−0.027, about 1' north-east of Sagittarius (Sgr) B2(N) carried out with the Yebes 40 m dish at 7 mm and with the IRAM 30 m dish at 3, 2, and 1 mm. The identified transitions cover the 2 to 7 mm regions 2 ≤ //J// ≤ 11 and //K<sub>a</sub>// ≤ 6 for //Ga// and 2 ≤ //J// ≤ 12 and //K<sub>a</sub>// ≤ 3 for //Aa//. The number of clean, slightly or partly blended transitions is sufficiently large for both conformers together and for //Ga// alone. The excitation temperature is about 13 K. //n//-Propanol is about a factor of 15 less abundant than ethanol which, in turn, is about a factor of 25 less abundant than methanol.\\
\\

 A. Belloche, R. T. Garrod, O. Zingsheim, H. S. P. Müller, and K. M. Menten\\
reported on the\\
**[[https://doi.org/10.1051/0004-6361/202243575|Interstellar Detection and Chemical Modeling of iso-Propanol and its normal Isomer]]**\\
//Astron. Astrophys.// **662** (2022), Art. No. A110.\\ 
2-Propanol was detected in the course of the ReMoCA 3 mm line survey of Sgr B2(N) carried out with ALMA toward a position Sgr B2(N2b) slightly offset from the dust continuum of Sgr B2(N2) and described here for the first time. Four (largely) unblended transitions were detected for the gauche conformer with 12 ≤ //J// ≤ 16 and //K<sub>a</sub>// ≤ 1 and three with 8 ≤ //J// ≤ 11 and //K<sub>a</sub>// ≤ 2 for anti.\\

The authors also reported the first detection of //n//-propanol in a star-forming region. Interestingly, eight transitions of the higher lying //Gg'// conformer with 8 ≤ //J// ≤ 12 and //K<sub>a</sub>// ≤ 4 and five transitions  of the higher lying //Ag// conformer with 12 ≤ //J// ≤ 15 and //K<sub>a</sub>// ≤ 6 were detected. Transitions of the lower lying conformers were also present, but all were blended more or less severely. Rotational temperatures of 135 K were inferred. The iso to normal ratio is about 0.6, fairly similar to the 0.4 ratio in the case of the two propyl cyanide isomers. In addition, //n//-propanol is about a factor of 18 less abundant than ethanol which, in turn, is about a factor of 19 less abundant than methanol.\\
\\
The Max-Planck-Institut für Radioastronomie issued a press release in **[[https://www.mpifr-bonn.mpg.de/pressreleases/2022/10?c=9060|English]]** and in **[[https://www.mpifr-bonn.mpg.de/pressemeldungen/2022/10?c=8727|German]]**. Similar press releases were issued by the **[[https://www.mpg.de/18884791/sanitizer-in-the-galactic-centre-region|Max Planck Society]]** and by the **[[https://portal.uni-koeln.de/en/universitaet/aktuell/press-releases/single-news/a-sanitizer-in-the-galactic-centre-region|Universität zu Köln]]**.


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Contributor(s): H. S. P. Müller; 06, 2022

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