Microwave-submillimeter wave double-resonance spectrometer for the investigation of van der Waals complexes

A double-resonance spectrometer, suitable for the investigation of low lyin g intermolecular vibrational modes and of tunneling transitions of van der Waals complexes, is described. The instrument utilizes a pulsed molecular b eam Fourier transform microwave spectrometer (frequency range 4-26 GHz) for signal detection, and a high frequency, phase stabilized, backward wave os cillator (258 - 375 GHz), as well as a millimeter wave synthesizer (78 - 11 8 GHz), as pump radiation sources. A brief description of the Fourier trans form microwave spectrometer and of the phase stabilization system of the ba ckward wave oscillator is given. The experimental arrangement is such that the molecular ensemble travels through the submillimeter radiation field pr ior to the pulsed excitation microwave experiment, in which the resulting p opulation changes are detected. The sensitivity and the resolution capabili ties of the new technique are illustrated with double resonance spectra of the van der Waals complexes Ar-CO and CO-N-2. (C) 1998 American Institute o f Physics. [S0034-6748(98)01312-4].