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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, ethyl methyl ether, also known as methoxyethane (CH3OC2H5), 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 CH3 group and by the OH group. The anti conformation refers to a dihedral angle of 180o with respect to the CCO plane, whereas the gauche conformations refer to a dihedral angle of ±60o. 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+ and Ag− 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−1 higher in energy. Tunneling within g leads to g+ and g− 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
Precursors of Fatty Alcohols in the ISM: Discovery of //n//-Propanol
Astron. Astrophys., (2022), in press.
Transitions of the Ga and Aa conformers of 1-propanol were observed in the course of a molecular line survey of the quiescent giant molecular cloud G+0.693−0.027, about 1' north-east of Sagittarius 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 0 ≤ Ka ≤ 6 for Ga and 2 ≤ J ≤ 12 and 0 ≤ Ka ≤ 3 for Aa. The number of clean, slightly or partly blended transitions is sufficiently large for both conformers together and for Ga alone.
A. Belloche, R. T. Garrod, O. Zingsheim, H. S. P. Müller, and K. M. Menten
reported on the
Interstellar Detection and Chemical Modeling of iso-Propanol and its normal Isomer
Astrophys. J. Lett. 662 (2022), Art. No. A110.
Contributor(s): H. S. P. Müller; 06, 2022