A Supersonic Jet Spectrometer for Terahertz Applications (SuJeSTA)

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The purpose of this work is to perform high resolution spectroscopic mea- surements in the terahertz region aiming at molecular parameters, derived from quantum mechanical analysis of the spectra. These parameters are the basic requirement for accurate frequency predictions and for the astronomi- cal detections of undiscovered species. Two di erent spectrometers have been used for the spectral analysis in this work: ˆ The newly designed Supersonic Jet Spectrometer for Terahertz Appli- cations (SuJeSTA) for the investigation of cold radicals and ions ˆ The Cologne Terahertz Spectrometer The pure rotational spectra of ve isotopomers of potassium chloride, i.e. 39K35Cl, 39K37Cl, 41K35Cl, 41K37Cl, and 40K35Cl have been recorded with the well established Cologne Terahertz Spectrometer (see e.g. ¹, ²). A special evaporation cell has been used to evaporate solid KCl. Within the scope of this thesis, a total of 295 new rotational lines have been measured in the fre- quency region between 170 and 930 GHz. For the isotopomers 39K35Cl and 39K37Cl 107 and 82, respectively, rotational transitions have been assigned to transitions belonging to vibrational levels up to the seventh excited state (v≤7) and to rotational quantum numbers as high as 127 and 129, respec- tively. 104 lines were measured for the less abundant isotopomers of 41K35Cl and 41K37Cl with J ≤ 128, v ≤ 6 and J ≤ 131, v ≤ 5, respectively. Two lines have been assigned to 40K35Cl, which has a natural abundance of 0.01% relative to 39K35Cl. The measured lines have been tted together with previously published millimeter wave transitions to obtain an improved set of molecular parameters for these isotopomers ³. Besides this analysis, the isotopically invariant Dunham parameters Uij and the Born-Oppenheimer corrections ∆01 have been determined. The re ned and extended parameter set allows precise predictions in the terahertz region. Structural parameters, such as the bond length and the moment of inertia, have been derived from the spectroscopic parameters.