15min:

Y. KAWASHIMA, Department of Applied Chemistry, Kanagawa Institute of Technology, Atsugi, Kanagawa 243-0292, JAPAN ; Y. OHSHIMA, Department of Chemistry, Kyoto University, Kyoto 606- 8502, JAPAN ; Y. ENDO, Graduate School of Art and Science, University of Tokyo 153-8902, JAPAN.

Observations of the infrared spectra of N₂--CO by diode laser spectroscopy have been reported previously . The present study is an observation of the rotational spectra of ¹⁴N₂--CO, ¹⁵N¹⁴N--CO, and ¹⁵N₂--CO using a Fourier transform microwave spectrometer. Two sets for the J = 2-1, 3-2, and 4-3 transitions are observed for ¹⁴N₂--CO and ¹⁵N₂--CO, while only one set for ¹⁵N¹⁴N--CO. The hyperfine structures are observed for the complexes containing ¹⁴N nucleus. The first set is assigned to the K=0 state of ortho-N₂ and the second to the K=1 state of para-N₂,based on the infrared analysis and eQq splittings. The transitions with the K=1 state are stronger than those with the K=0 state for ¹⁴N₂--CO complex, while the reversed is observed for ¹⁵N₂--CO. In the case of ¹⁵N¹⁴N--CO only lowest transition is observed because of lack of symmetry in the complex. The nuclear electric quadrupole coupling constant of the ¹⁴N nucleus is much smaller than related complexes. The value of the van der Waals stretching frequency for N₂--CO is calculated to be 19 cm^-1 from the rotational and the centrifugal distortion constants obtained. We concluded that both moieties, N₂ and CO, are rotating almost freely in the complex N₂--CO.