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Spectra of the nitrous oxide dimer (N2O)2 are studied in the region of the N2O nu1 fundamental band around 2230 cm-1 using a rapid-scan tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. The previously known band of the centrosymmetric nonpolar dimer is analyzed in improved detail, and a new band is observed and assigned to a polar isomer of (N2O)2. This polar form of the dimer has a slipped parallel structure, rather similar to the slipped antiparallel structure of the nonpolar form but with a slightly larger intermolecular distance. The accurate rotational parameters determined here should enable a microwave observation of the polar N2O dimer. The need for a modern ab initio investigation of the N2O-N2O intermolecular potential energy surface is emphasized.

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A new infrared band at 2069.3 cm-1 is observed and assigned to the long-anticipated polar isomer of the OCS dimer, helping to explain apparent discrepancies among earlier studies. The data reported here should enable direct observation of the microwave spectrum of polar (OCS)2 and motivate new theoretical works on the energetics of OCS dimer isomers and interconversion energy barriers.

Improved quantum chemistry (coupled-cluster) results are presented for spectroscopic parameters and the potential energy surface for the N(2)O dimer. The calculations produce three isomer structures, of which the two lowest energy forms are those observed experimentally: a nonpolar C(2h)-symmetry planar slipped-antiparallel geometry (with inward-located O atoms) and a higher-energy polar C(s)-symmetry planar slipped-parallel geometry. Harmonic vibrational frequencies and infrared intensities for these isomers are calculated. The low-frequency intermolecular vibrational mode predictions should be useful for future spectroscopic searches, and there is good agreement in the one case where an experimental value is available. The frequency shifts for the high-frequency intramolecular stretching vibrations, relative to the monomer, were calculated and used to help locate a new infrared band of the polar isomer, which corresponds to the weaker out-of-phase combination of the nu(1) antisymmetric stretch of the individual monomers. The new band was observed in the region of the monomer nu(1) fundamental for both ((14)N(2)O)(2) and ((15)N(2)O)(2) using a tunable infrared diode laser to probe a pulsed supersonic jet expansion, and results are presented.