A MICROWAVE FREE JET ABSORPTION SPECTROMETER AND ITS FIRST APPLICATIONS

A free jet absorption microwave spectrometer working in the frequency range 50-80 GHz has recently been built in our laboratory. Different e xperiments can be performed with the system: the microwave radiation c an be focussed on the supersonic expansion either with a lens correcte d horn system or with a semiconfocal Fabry-Perot interferometer. The m icrowave radiation can be either parallel or perpendicular to the jet, and Stark modulation or double resonance experiments (MW-MW or RF-MW, respectively) are possible. As first applications, studies on complic ated conformational equilibria, tautomeric equilibria and molecules wi th puzzling nuclear hyperfine structure (for example, a molecule conta ining two iodine atoms) have been performed.