Development of Millimeter-wave Spectrometer Combined with the Supersonic Pulsed Jet Expansion

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The millimeter-wave spectrometer combined with pulsed supersonic jet expansion technique has been devised to measure the van der Waals (vdW) vibration transitions of molecular clusters by direct absorption observation method.The spectrometer was applied to the measurement of rovibrational transitions in the van der Waals band of ArHCN near 200 GHz for both the SIGMA_1-SIGMA_0 and PI_1-SIGMA_0 subbands. The technique has been extended to the vdW hot band transitions (j=2-1) of ArHCN and the fundamental vdW bending band of the ArDCN isotopic species. A precise set of molecular constants, including the band origins, rotational constants, quadrupole coupling constant, and Coriolis coupling constants, was derived to detemine the potential function between Ar and HCN.The technique was also applied to observe the pure rotational transitions of ArDCN and the dueterated HCN dimmers in the microwave region.The spectrometer was combined with discharge nozzle to detect the transient species cooled in the supersonic jet expansion. The pure rotational spectra of the CS and CN radicals and the DCO^+ ion have bee observed in the millimeter-wave region.The new submillimeter-wave spectrometer with Backward Oscillator (BWO) was set up to observe the vdW transitions in the higher frequency region.