HIGH RESOLUTION SPECTRA OF CARBON DIOXIDE CLUSTERS IN THE \nub{3} BAND REGION

Abstract

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 (CO$_2$)$_2$ and (CO$_2$)$_3$. The dimer has a planar slipped parallel geometry with $C_{2h}$ symmetry. \textbf{86}, 4341 (1987); M.A. Walsh, T.H. England, T.R. Dyke, and B.J. Howard, \textit{Chem. Phys. Lett.} \textbf{142}, 265 (1987).} Two isomers are known for the trimer: a planar cyclic form with $C_{3h}$ symmetry \textbf{87}, 1502 (1987).} and a sort of ``barrel-shaped" form with $C_2$ symmetry. \textbf{105}, 10210 (1996).} Here we analyze two new bands in the CO$_2$ \nub{3} region. The first is a dimer combination band near 2382 $\wn$ whose assignment raises interesting questions about the intermolecular vibrations of (CO$_2$)$_2$. \textbf{112}, 5070 (2000).} The second band is a trimer band near 2370 $\wn$ which is very similar to one we observed previously near 2364 $\wn$. \textbf{128}, 064308 (2008).} 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 (CO$_2$)$_N$ clusters with $N$ in the range 6 $\sim$ 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 CO$_2$ clusters in a challenging and important size range.