U. Fuchs

trans-Ethyl Methyl Ether: Assignments and Predictions up to 400 GHz for the Vibrational-Torsional Ground State

Ethyl methyl ether (C2H5OCH3) has been tentatively detected in hot cores, which are quiescent high-density sources associated with regions of high-mass star formation. Up to now, the only published laboratory rotational-torsional transitions for this molecule lie at frequencies under 35 GHz. In this paper, we report the measurement and assignment of many rotational-torsional transitions of ethyl methyl ether in its vibrational-torsional ground state at frequencies through 350 GHz. A fit to experimental accuracy of over 1000 new and previously assigned transitions has allowed us to predict the frequencies of many additional transitions up to 400 GHz. The results of this work should enable astronomers to confirm the existence of ethyl methyl ether in interstellar sources.

High resolution spectroscopy of HCN isotopomers: H13CN, HC15N, and H13C15N in the ground and first excited bending vibrational state

The eleven energetically lowest pure rotational transitions, J ←J−1 (J =1,2, . . . ,11), of H13CN, H13C15N, and HC15N in the ground and first excited bending state were measured. By operating the Cologne Tetrahertz Wave Spectrometer up to 1 THz in the sub-Doppler mode, a transition frequency accuracy of a few kHz is achieved. These measurements were carried out at frequencies between 80 - 950 GHz. In addition, some transitions of the three isotopomers with rotational quantum numbers J = 20,21,22,23 have been measured in Doppler-limited resolution near 2 THz, using the frequency stabilized Cologne Sideband Spectrometer for Terahertz Applications (COSSTA). Furthermore, direct l-type transitions of H13CN in the first excited bending state with J up to 35 have been measured. These new data are of particular importance, since we discovered highly excited circumstellar H12CN recently. A global fit of the newly enlarged data set together with existing carefully screened ro-vibrational data yields molecular constants which are highly reliable and of great importance both for astrophysical observations and laboratory applications

Spectroscopy of Linear Carbon Chain Radicals — The Case of C n N Chains

Carbon chains are the dominant architectural scheme of interstellar molecular chemistry. The cyano radicals C3Nand C5N, for example, have been detected in the late type star IRC+10216 and in the molecular cloud TMC-1; C3N also in IRAS 15194-5115, TMC-2, HCL 2, CRL618, and CRL2688 ([1], Appendix D). Other cyano radicals like C2N with a much smaller dipole moment have not been observed so far. The astronomical detection of these species depends strongly on the knowledge of their transition frequencies obtained by laboratory work. Longer CnN chains or isotopomers of CnN are difficult to observe in the laboratory and very sensitive spectrometers are required to detect their transition frequencies.

Terahertz Rotational Spectroscopy

The detection of interstellar molecules relies on the precise knowledge of spectral line positions from laboratory measurements. Technical developments of recent years have led to an extension of the accessible spectral range towards shorter wavelengths. New telescopes like SOFIA, the HIFI instrument aboard the Herschel satellite, and ALMA will be used for astrophysical observations in the terahertz region. The Cologne group has developed precise spectrometers to study molecules of astrophysical importance under laboratory conditions and to obtain characteristic spectra for their possible detection in space. We present recent results on light hydrides, carbon-chain molecules and more complex species.