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C3H8O2  –  1,2-propanediol


  • zakharenko
  • lewen
  • hspm


The simplest sugar-type molecule glycoaldehyde (CH2OHCHO) and its sugar alcohol ethylene glycol (HOCH2CH2OH) have been detected toward Sagittarius B2(N-LMH). It has been suggested that the aldehyde and their reduced alcohol pairs can shed light on the processes of complex interstellar molecule formation, namely that such molecules are produced from a low-temperature chemistry occurring on dust grain surfaces or in grain ice mantles. Propanediols are derivatives of ethanediol, therefore it is the next potential candidate for detecting in the interstellar medium. ...more


Absorption Rotational Spectroscopy
Rotational spectroscopy is a key method to investigate molecules, radicals and ions. These species are capable of motions, in particular molecular rotation. If a permanent or induced dipole moment is existent, the species is called transient and the underlying energy states are quantized and accessible for electromagnetic waves. The energy distances between the rotational levels are such, that mostly the transition lines are in the cm- (up to 30 GHz), mm- (up to 300 GHz) and in part shorter wavelength ranges of the electromagnetic spectrum. Since the energies necessary to excite the rotational states are low, the typical temperatures in the ISM are sufficiently high for exiting these states (T = 5 K to much more than 100 K). The line frequencies of the transitions can be measured with great accuracy; this, in turn, gives precise molecular parameters, which allows calculating reliable predictions of new molecular lines which helps to identify new molecular species in space. Such line lists and the parameters of many species are available in our Cologne Database for Molecular Spectroscopy (
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With its exceptionally long absorption path, MIDAS-COINS is enhancing our sensitivity in the millimeter range since 2010.
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Recent Results

Lovas et al (2009) studied the rotational spectra of the seven lowest energy conformers of 1,2-propanediol by Fourier transform microwave (FTMW) spectroscopy and determined relative energies through quantum chemical calculations. The data were insufficient for astronomical searches in the dense and warm parts of star-forming regions where 1,2-propanediol has the greatest chance of being detected. Therefore, we have carried out a new study of the rotational spectrum of 1,2-propanediol in three frequency bands, 38 – 70, 200 – 230 and 297 – 400 GHz. The ground state rotational transitions have been analysed up to sufficiently high J and Ka quantum numbers to provide accurate predictions for the millimetre-wave frequency region for the astronomical purposes. The analysis of the rotational spectra of 1,2-propanediol conformers was performed as regular asymmetric top molecule using the Pickett’s programs SPFIT for the fitting and SPCAT for predicting line positions. Watson’s S-reduced Hamiltonian was used for fitting rotational transitions. Bossa et al. (2014) reported greatly extended analyses of the three lowest energy conformers. Zakharenko et al. (2017) presented results on the four conformers next higher in energy. The search for conformers even higher in energy continues.
Figure 2: Section of the rotational spectrum of 1,2-propanediol near 223 GHz. The line intensity of g´Gg (375 cm-1) higher than the lowest energy conformer) is much weaker compared to the lower gG´g´ (230 cm-1) and g´G´a (212 cm-1) conformers. The unassigned lines belong mainly to excited states of lower energy conformers.
Figure 3. The 538,45-528,44 transition of the aG´g conformer occurs at 333 812.0 MHz, but it is overlapped by a stronger, unidentified line (see*).


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  • The investigation has been funded by the Deutsche Forschungsgemeinschaft (DFG) within the Collaborative Research Centre 956 "Conditions and Impact of Star Formation", project B3, and through the Gerätezentrum "Cologne Center for Terahertz Specroscopy".
  • J.B.B. is grateful for support from the Marie Curie Intra-European Fellowship (FP7-PEOPLE-2011-IEF-299258).