Vibrationally excited states in a pulsed jet observed by Fourier transform microwave spectroscopy

Rotational transitions of fluorobenzene in vibrationally excited states have been measured between 7 and 17 GHz with a pulsed nozzle Fourier transform microwave spectrometer. Despite the strong cooling in the supersonic expansion, some vibrations have not been depopulated below the detection limit. The intensities of these transitions have been studied in relation to choice of the rare gas used as carrier and to the stagnation pressure. The results have been compared to those obtained using a static gas sample at ambient temperature.