Microwave spectroscopy of molecular complexes

Weakly bound molecular complexes are formed in supersonic expansions of seeded rare gases. Their rotational spectra have been observed with pulsed nozzle Fourier transform microwave spectrometers. The analysis of the rotational spectra, usually including isotopic variants of the complexes, has provided valuable information about the geometric structure of complexes. When complexes are formed the loss of translational and rotational degrees of freedom of the monomers leads to low-frequency Van der Waals vibrations. Often, tunneling motions between equivalent minima of the intermolecular potential energy surface have complicated the interpretation of the microwave spectra considerably. Centrifugal distortion and tunnel splittings have given important insights into the intermolecular dynamics. (C) 1997 Elsevier Science B.V.