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Universität zu Köln
Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Research Projects

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Dimethyl ether is known to be a prominent molecule in star forming regions. Owing to its strong and dense spectrum throughout the entire microwave and terahertz regime, it contributes to the spectral confusion in astronomical line surveys. The latest generation of telescopes like the Atacama Large Millimeter Array (ALMA) enhance the need for accurate prediction of transition frequencies and intensities in the terahertz region. Owing to the increased sensitivity of these observing facilities, predictions are also required for vibrationally excited states of promient molecules like dimethyl ether. ...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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{Millimeterwave Spectrometer}
{Superlattice Spectrometer}

Recent Results

New laboratory absorption spectra on dimethyl ether's main isotopologue 12CH3O12CH3 were obtained from 38 GHz to almost 2.1 THz. The existing dataset of rotation-torsion transitions within the vibrational ground state was greatly extended. Furthermore the two lowest excited torsional states of dimethyl ether were investigated. The analysis yields predictions for the rotational transitions up to about 2 THz with an accuracy of better than 1 MHz. Based on the laboratory analysis, transitions of dimethyl ether in its torsionally excited states, ν11 = 1 and ν15 = 1 were detected for the first time in the interstellar medium towards the high-mass star-forming region G327.3-0.6.
Details of the line survey of G327.3-06 carried out with the APEX telescope. The observation is depicted in black, the modeled spectrum of previously identified species is overplotted in blue, whereas the modeled dimethyl ether spectrum is shown in red color (see Bisschop et al. 2013).


External Links


  • The investigation of dimethyl ether has been carried out within the Collaborative Research Centre 956, sub-project B3, funded by the Deutsche Forschungsgemeinschaft (DFG).