Knowledge Bank

An experimental, Stark-modulated microwave spectrometer has been constructed in X-band (using a waveguide absorption cell) which measures the absolute intensity coefficient of the narrow, weak absorption lines characteristic of gas-phase microwave spectroscopy. Some of the features of this spectrometer include a phase-locked power leveled backward wave oscillator with direct readout of frequency to 1 Kc/sec in X-band, a modified bridge system with the absorption cell in one arm of the bridge, a third arm with a PIN diode modulator and precision attenuator for the absolute intensity measurements, ten Kc/sec Stark modulation frequency and crystal detectors with low 1/f noise at 10 Kc/sec. Some measurements have been taken on the $J=0\to J=1$ rotational transition of carbonyl sulfide. The absorption coefficient has been measured as a function of power for a variety of pressures. The line width parameter (half-width at the half-power point) has also been measured as a function of pressure. Using these saturation and line width data, the ratio between the line broadening and equilibrium restoring molecular collision rate will be discussed.