15min:

NICHOLAS R. WALKER, School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K.; ANDREA J. MINEI, STEWART E. NOVICK, Department of Chemistry, Wesleyan University, Middletown, Connecticut 06459, U.S.A.; AND ANTHONY C. LEGON, School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K..

Cavity Fourier-Transform microwave spectroscopy has been used to characterise a gas phase, polar dimer of N₂O. The polar (N₂O)₂ unit is generated by co-expansion of a gas sample containing a small percentage of N₂O in a helium backing gas. Transitions in the pure rotational spectra of (¹⁵N₂O)₂, (¹⁴N¹⁵NO)(¹⁵N₂O), (¹⁴N₂O)(¹⁵N₂O) and (¹⁴N₂O)₂ are reported. The measured transitions of (¹⁵N₂O)₂ and (¹⁴N¹⁵NO)(¹⁵N₂O) are assigned and fitted to Hamiltonians allowing rotational, centrifugal distortion and ¹⁴N nuclear quadrupole coupling constants to be determined. Hyperfine structure is assigned for a single J_K_-1'K₊₁'' J_K_-1''K₊₁'''' transition of both isotopomers of (¹⁴N₂O)(¹⁵N₂O). Nuclear quadrupole coupling constants, _bb, are reported for all four ¹⁴N nuclei. The measured _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)Å with the two N₂O monomers respectively oriented 54.69(68)^\circ and 49.85(64)^\circ to the a-inertial axis. Simulation of hyperfine structure in the spectrum of the (¹⁴N₂O)₂ isotopomer yields good qualitative agreement with experiment.