Caris, Michael

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Kölner UniversitätsPublikationsServer

AbstractThe purpose of this work is to perform high resolution spectroscopic mea-surements in the terahertz region aiming at molecular parameters, derivedfrom quantum mechanical analysis of the spectra. These parameters are thebasic requirement for accurate frequency predictions and for the astronomi-cal detections of undiscovered species. Two diﬀerent spectrometers have beenused for the spectral analysis in this work: The newly designed Supersonic Jet Spectrometer for Terahertz Appli-cations (SuJeSTA) for the investigation of cold radicals and ions The Cologne Terahertz SpectrometerThe pure rotational spectra of ﬁve isotopomers of potassium chloride, i.e.39K35Cl, 39K37Cl, 41K35Cl, 41K37Cl, and 40K35Cl have been recorded withthe well established Cologne Terahertz Spectrometer. A special evaporationcell has been used to evaporate solid KCl. Within the scope of this thesis, atotal of 295 new rotational lines have been measured in the frequency regionbetween 170 and 930 GHz. For the isotopomers 39K35Cl and 39K37Cl 107and 82, respectively, rotational transitions have been assigned to transitionsbelonging to vibrational levels up to the seventh excited state (v≤ 7) and torotational quantum numbers as high as 127 and 129, respectively. 104 lineswere measured for the less abundant isotopomers of 41K35Cl and 41K37Clwith J ≤ 128, v ≤ 6 and J ≤ 131, v ≤ 5, respectively. Two lines havebeen assigned to 40K35Cl, which has a natural abundance of 0.01% relativeto 39K35Cl. The measured lines have been ﬁtted together with previouslypublished millimeter wave transitions to obtain an improved set of molecularparameters for these isotopomers. Besides this analysis, the isotopically in-variant Dunham parameters Ui j and the Born-Oppenheimer corrections ∆01have been determined. The reﬁned and extended parameter set allows precisepredictions in the terahertz region. Structural parameters, such as the bondlength and the moment of inertia, have been derived from the spectroscopicparameters.A main task of this work was the construction and assembly of the newCologne Supersonic Jet Spectrometer for Terahertz Applications (SuJeSTA).2It is employed to record the spectra of radicals and ions which are producedin a pulsed discharge with a subsequent supersonic jet expansion to obtainadiabatically cooled molecules.The ﬁrst application of SuJeSTA has been an intensive investigation of thelinear X2Π propynylidyne radical, l−C3H. It is supposed to play a decisiverole in the carbon chain growth in the interstellar medium and has beensubject of astronomical observations and laboratory investigations. WithSuJeSTA the ν4 (2Σµ) CCH bending vibration of C3H has been recorded inthe submillimeter region for the ﬁrst time. Due to a strong Renner-Tellereﬀect the bending transitions lie in the submillimeter wavelength region.Eight measured lines have been assigned to ro-vibrational transitions betweenthe vibrational ground state (2Π) and the excited bending state v4= 1 (2Σµ).In addition, the pure rotational spectrum of C3H has been investigated up to600 GHz to extend the number of measured transitions. A total of 43 purerotational lines in the vibrational ground states (2Π1/2, 2Π3/2) and excitedstate v4 = 1 (2Σµ) have been recorded. Reliable frequency predictions up to1 THz are available due to a new set of spectroscopic parameters, obtainedfrom a least squares ﬁt to a standard Hamiltonian.Furthermore, the new spectrometer facilitates the production of ions. Inthe course of this thesis, transitions of CO+ have been recorded to provethe spectrometer's ability of ion production. An isotopically invariant ﬁt ofthe new data and data published previously resulted in a mass independentparameter set which describes the spectrum of the CO+ ion up to 1 THzwith high accuracy. Improved structural constants have been derived fromthe spectroscopic parameters. Interstellar CO+ is of crucial importance fortracing PDRs (Photon Dominated Region) and has been detected in space.All obtained data are reliable for frequency predictions up to 1 THz andare available via the Cologne Database for Molecular Spectroscopy (CDMS).

A Supersonic Jet Spectrometer for Terahertz Applications (SuJeSTA)

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