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Universität zu Köln
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Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

Research Projects

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13CH3OCH3  /  13CH3O13CH3  –  dimethyl ether

Investigators

  • koerber
  • endres
  • lewen

Description

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) with its unprecedented sensitivity enhance the need for accurate prediction of transition frequencies also for isotopologues of promient molecules like dimethyl ether. In addition, the investigation of the abundance ratio of isotopologues enables to get an insight on their formation mechanism. ...more

Methods

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. CDMS.de).
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Instruments

{Millimeterwave Spectrometer}
{Superlattice Spectrometer}
{Multiplier Chains}

Recent Results

The ground state transitions of dimethyl ether's 13C-isotopologues were recorded from 34 GHz up to 1.5 THz. For 13CH3O12CH3 the existing data by Niide & Hayashi (2003) were substantially extended. For 13CH3O13CH3 the first rotational spectroscopic data were obtained. 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 13CH3O12CH3 were detected for the first time in the interstellar medium towards the high-mass star-forming region G327.3-0.6.
Experimental spectrum of the transition JKa,Kc = 143,11←134,10 for all three carbon isotopologues of dimethyl ether. The spectrum displays the splitting into several torsional components. Spin statistical weight factors are given in parentheses behind the substate designation.
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. The spectroscopic assignment of the transitions is given in the upper left corner of each panel. (see Koerber et al. 2013)

Publications

External Links

Acknowledgments

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