FIRST EXPERIENCES WITH AN AUTOMATIC PULSED MOLECULAR BEAM MICROWAVE FOURIER TRANSFORM SPECTROMETER

Author Institution: Institute f\""{u}r Physikalische Chemie, Universit\""{a}t KielThe pulsed molecular beam microwave Fourier transform (MB-MWFT) spectrometer turned out to be an extremely useful tool for the assignment of microwave spectra of stable as well as under normal conditions unstable molecules. This advantage arises mainly from the fact that in the molecular beam the rotational temperature is in the order of some Kelvin and therefore only a few low lying energy levels are populated which results in a rather clear rotational spectrum. Due to the narrow bandwidth of the microwave cavity one usually observes only a small range of the spectrum in a single experiment. This disadvantage makes it rather tedious to scan wide frequency ranges if a completely unknown spectrum is to be measured, because the cavity has to be tuned manually after each single measurement. We now automated this process. The whole measuring sequence including the tuning of the cavity is computer controlled and after each measurement significant spectral lines are detected and recorded. This greatly increased the efficiency of the MB-MWFT spectrometer and gives more time to the spectroscopist to assign his spectra while the apparatus scans hundreds of MHz automatically. Technical details of the MB-MWFT spectrometer of the University of Kiel and an application of the automatic scanning facility for the measurement and a assignment of the rotorsional spectrum of tert-Butyl isocyanate will be presented in the tal