Rotational spectrum of the N2··CO complex: ortho-N2 and para-N2

Pure rotational spectra of 14N2··CO, 15N14N··CO, and 15N2··CO have been observed using a Fourier transform microwave spectrometer. Two sets of transitions with J=2←1, 3←2, and 4←3 were observed for 14N2··CO and 15N2··CO; transitions with smaller effective rotational constants B were stronger than those with larger B for the 14N2··CO complex, while the opposite was observed for 15N2··CO. It was concluded that for 14N2··CO the first set corresponds to the K=0 stack of ortho-N2 and the second to K=1 of para-N2 based on a previous infrared analysis, hyperfine splittings, and the spin statistical weights. In the case of 15N14N··CO, only one set was observed because of the lack of symmetry. The electric quadrupole coupling constant of 14N is much smaller, while the centrifugal distortion constant is much larger, than those of related complexes.