The Far Infrared Spectrum of the NO Dimer

ISSN： 0022-2852

Source： Journal of Molecular Spectroscopy, Vol.194, Iss.2, 1999-04, pp. : 229-235

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Abstract

The far-infrared spectrum of the NO dimer in the gas phase has been observed for the first time using a long-path (180 m) cooled (99 K) absorption cell and a Bomem Fourier transform spectrometer. Four weak vibration–rotation bands were detected in the 120–450 cm^-1region and assigned to intermolecular vibrations of thecis–planar ON–NO complex. The strongest is a typebband at 239.36 cm^-1, which is assigned as the ν₂(symmetric bending) fundamental. A second typebband at 134.50 cm^-1, partly obscured by²Π_3/2←²Π_1/2transitions of the NO monomer, is assigned as the ν₃(intermolecular stretch) fundamental. A third typebband at 351.38 cm^-1can then be assigned as the ν₂+ ν₃combination band. Finally, a very weak typeaband at 429.14 cm^-1is assigned as the ν₆(antisymmetric bending) fundamental. We report here detailed analyses of the ν₂and ν₂+ ν₃bands, which yielded upper state rotational parameters, centrifugal distortion parameters, and band origins. Somewhat less extensive analyses for ν₃and ν₆give their rotational parameters and band origins. These results resolve the mystery of the true values of the intermolecular vibrational frequencies of the NO dimer, which turn out to be rather different from previous determinations based on condensed phase spectra.