Pure rotational spectra of the van der Waals complexes Ne–CO, Kr–CO, and Xe–CO

Abstract

The pure rotational spectra of the van der Waals dimers of Ne, Kr, and Xe with CO have been measured using a pulsed jet, cavity microwave Fourier transform spectrometer. All transitions measured were a-type R-branches, obeying selection rules ΔJ=+1, ΔKa=0, and ΔKc=+1. Spectra with Ka=0 were measured for 7 isotopomers of Ne–CO, 13 of Kr–CO, and 17 of Xe–CO. Transitions with Ka=1 were measured for Ne20–C12O16 and Kr-84C12O16. Rotational constants and centrifugal distortion constants have been determined for all species, as well as the O17 quadrupole coupling constants χaa for Kr-184C13O17 and Ne20C13O17. Effective structural parameters have been calculated from the rotational constants. Results derived from the O17 quadrupole coupling constants and centrifugal distortion constants indicate that Ne–CO is considerably more flexible than Ar–CO, Kr–CO, or Xe–CO. Failure to observe hyperfine structure due to the Ne21, Kr83, and Xe131 nuclei is discussed in terms of the weak rare gas–CO bonding. Comparisons have been made to the isoelectronic rare gas–N2 van der Waals complexes.