Transient frequency-modulation absorption spectroscopy of free radicals in supersonic free jet expansions

A new technique combining supersonic jet expansion and transient frequency-modulation absorption experiments has been successfully developed for spectroscopic investigations of free radicals. The à ← X̃ transition spectra of NH2 and HCCl at near-infrared wavelengths have been obtained using this technique for demonstration. In addition, a combination of temporal waveform acquisition and frequency scan using this new technique has produced interesting information on the velocity and density distributions of supersonic jet expansion systems.