15min:

A. R. W. MCKELLAR, Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada; MAHIN AFSHARI, M. DEHGHANY AND N. MOAZZEN-AHMADI, Department of Physics and Astronomy, University of Calgary, 2500 University Dr., N.W., Calgary, AB T2N 1N4, Canada.

There is widespread interest in carbon dioxide clusters from a variety of experimental and theoretical perspectives. But in terms of high resolution spectroscopy, the only definitive information concerns (CO₂)₂ and (CO₂)₃. The dimer has a planar slipped parallel geometry with C_2h symmetry.\footnote[1]K.W. Jucks, Z.S. Huang, D. Dayton, R.E. Miller, and W.J. Lafferty, J. Chem. Phys. \textbf86, 4341 (1987); M.A. Walsh, T.H. England, T.R. Dyke, and B.J. Howard, Chem. Phys. Lett. \textbf142, 265 (1987). Two isomers are known for the trimer: a planar cyclic form with C_3h symmetry and a sort of ``barrel-shaped" form with C₂ symmetry.

Here we analyze two new bands in the CO_{2 3} region. The first is a dimer combination band near 2382 cm^-1 whose assignment raises interesting questions about the intermolecular vibrations of (CO₂)₂. The second band is a trimer band near 2370 cm^-1 which is very similar to one we observed previously near 2364 cm^-1. We assign it to a combination involving another out-of-plane vibration of the cyclic trimer. In addition to these newly assigned bands, we also discuss a number of clear and (mostly) well-resolved bands which apparently must belong to (CO₂)_N clusters with N in the range 6 15. Although they cannot be precisely assigned at this time, these bands offer intriguing future prospects for learning more about the structures and vibrational dynamics of CO₂ clusters in a challenging and important size range.