ROTATIONAL SPECTRA OF PYRIDINE-(ARGON)(N), N=1, 2, COMPLEXES AND THEIR VIBRATIONALLY AVERAGED STRUCTURES

Rotational spectra of the van der Waals complexes of pyridine-N-14- an d pyridine-N-15-(argon)(2) have been observed in a pulsed nozzle Fouri er transform microwave spectrometer over the frequency range 8-18 GHz. In addition, pyridine-N-15- and pyridine-d(5)-argon complexes have be en investigated. The rotational spectrum of the pyridine-d(5) monomer has been measured in a conventional Stark spectrometer. The structures of both types of complexes have been determined, accounting for large -amplitude van der Waals vibrations. A C-s symmetric structure has bee n found with the argon above the ring plane at a distance of 3.545(1) Angstrom from the center-of-mass of pyridine and including an angle of 3.2(4)degrees with the principal axis c of pyridine. The second argon assumes a symmetrically equivalent position below the ring plane wher e the angles are increased slightly to 3.92(4)degrees, indicating negl igible three-body effects.