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M. DEHGHANY, MAHIN AFSHARI, J. N. OLIAEE, N. MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, CANADA; A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, CANADA.
Infrared spectra of N2O trimers are studied using a tunable diode laser to probe a pulsed supersonic slit-jet expansion. A previous observation by R.E. Miller and L. Pedersen [J. Chem. Phys. \textbf108, 436 (1998)] in the N2O
1+
3 combination band region (~3480 cm-1) showed the trimer structure to be noncyclic, with three inequivalent N2O monomer units which could be thought of as an N2O dimer (slipped antiparallel configuration) plus a third monomer unit lying above the dimer plane. The present observations cover the N2O fundamental band regions
3 (~1280 cm-1) and
1 (~2230 cm-1). In the
3 region, two trimer bands are assigned with vibrational shifts and other characteristics similar to those in the
1+
3 region, but in the
1 region all three possible trimer bands are observed. Relationships among the various bands such as rotational intensity patterns, vibrational shifts, and the properties of the related N2O dimer, generally support the conclusions of Miller and Pedersen. Three trimer bands are also observed for the fully 15N-substituted species in the
1 region, and these results should aid in detection of the as-yet-unobserved pure rotational microwave spectrum of the trimer. Finally, three combination bands involving the intermolecular van der Waals modes at 2253.7, 2255.5, and 2269.4 cm-1 have been measured. The analyses of these bands and the identification of the nature of the intermolecular modes involved are currently underway.