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

Pulsed nozzle Fourier transform microwave spectroscopy has been used to observe the rotational spectrum of the furan-3,4-d(2)-(argon)(2) van der Waals complex. The rotational spectra of the furan-3-d-, furan-3,4-d(2)-, and furan-(d4)-argon complexes have been measured in addition to the two previously measured isotopomers furan- and furan-2-d-argon. Rotational and quartic centrifugal distortion constants have been fitted for each isotopomer. Deuterium quadrupole coupling constants have been determined for the furan-3-d-argon complex from hyperfine splittings of the rotational transitions. A model considering the effects of large-amplitude van der Waals vibrations has been used for the determination of the intermolecular structural parameters. Argon has been located at a distance R = 3.539(2) Angstrom from the center-of-mass of furan for the furan-argon complex. Argon has been found shifted towards the oxygen including an angle theta = 9.7(2)degrees between R and the principal axis c of furan. In the furan-(argon)(2) complex, the two argon atoms assume symmetrical positions above and below the plane of furan with R and theta almost unchanged compared with the furan-argon complex.