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Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

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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 cm- (up to 30 GHz) and mm- (up to 300 GHz) wavelength range 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 > 100 K). The line frequencies of the transitions can be measured with great accuracy; this in turn gives precise molecular constants, which allows calculating reliable predictions of new molecular lines which helps to indentify new molecular species in space. Such line lists and constants for many species are available in our Cologne Database for Molecular Spectroscopy (www.
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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

We have carried out the new study of the rotational spectrum of seven lowest energy conformers 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.
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).