Nitrous oxide dimer: An ab initio coupled-cluster study of isomers, interconversions, and infrared fundamental bands, and experimental observation of a new fundamental for the polar isomer

Improved quantum chemistry (coupled-cluster) results are presented for spectroscopic parameters and the potential energy surface for the N2O 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 ((N2O)-N-14)(2) and ((N2O)-N-15)(2) using a tunable infrared diode laser to probe a pulsed supersonic jet expansion, and results are presented. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3121224]