Millimeterwave spectroscopy of transient molecules produced in a DC discharge

The construction of a millimeterwave spectrometer to study the pure rotational spectra or transient molecules in the gas phase is presented. The spectrometer is a source-modulated system combined with a free space glass discharge cell. Millimeterwave radiation has been produced using a frequency multiplier, the fundamental radiation sour e being klystrons. The spectrometer has been used to study the millimeterwave spectrum of carbon monosulfide (CS) and fluorine cyanide (FCN) produced inside the cell in a low pressure DC discharge of precursor gases. The quadrupole hyperfine structures of S-33 and N-14 nucleus of CS and FCN have been resolved, measured and analysed.