Microwave spectrum and structure of the polar N2O dimer

Cavity Fourier-transform microwave spectroscopy has been used to characterise a gas phase, polar dirtier of N2O. The polar (N2O)(2) unit is generated by co-expansion of a gas sample containing a small percentage of N2O in helium backing gas. Transitions in the pure rotational spectra of ((N2O)-N-15)(2), ((NNO)-N-14-N-15)((N2O)-N-15), ((N2O)-N-14)((N2O)-N-15) and ((N2O)-N-14)(2) are reported. The measured transitions of ((N2O)-N-15)(2) and ((NNO)-N-14-N-15)((N2O)-N-15) are assigned and fitted to Hamiltonians allowing rotational, centrifugal distortion and N-14 nuclear quadrupole coupling constants to be determined. Hyperfine structure is assigned for a single J'KK'-1'(+1) -> J ''(K '' 1K ''+1) transition of both isotopomers of ((N2O)-N-14)((N2O)-N-15). Nuclear quadrupole coupling constants, chi(bb), are reported for all four N-14 nuclei. The measured chi(bb) are in excellent agreement with those structures predicted from the measured rotational constants. The geometry of the molecule is slipped-parallel. The separation between the central nitrogen nuclei of the monomers in the r(m)((1)) structure is 3.570(12) angstrom with the two N2O monomers, respectively, oriented 54,69(68)degrees and 49.85(64)degrees to the a-inertial axis. Simulation of hyperfine structure in the spectrum of the ((N2O)-N-14)(2) isotopomer yields good qualitative agreement with experiment. (c) 2008 Elsevier Inc. All rights reserved.