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

Abstract

A double-resonance spectrometer, suitable for the investigation of low lying intermolecular vibrational modes and of tunneling transitions of van der Waals complexes, is described. The instrument utilizes a pulsed molecular beam Fourier transform microwave spectrometer (frequency range 4–26 GHz) for signal detection, and a high frequency, phase stabilized, backward wave oscillator (258–375 GHz), as well as a millimeter wave synthesizer (78–118 GHz), as pump radiation sources. A brief description of the Fourier transform microwave spectrometer and of the phase stabilization system of the backward wave oscillator is given. The experimental arrangement is such that the molecular ensemble travels through the submillimeter radiation field prior to the pulsed excitation microwave experiment, in which the resulting population changes are detected. The sensitivity and the resolution capabilities of the new technique are illustrated with double resonance spectra of the van der Waals complexes Ar–CO and CO–N2.