CARBON DIOXIDE CLUSTERS: (CO$_2$)$_6$ TO (CO$_2$)$_{13}$
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Date
2011
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
We recenty reported \textbf{13}, 1297 (2011).} assignments of specific infrared bands in the CO$_2$ \nub{3} region ($\sim$2350 $\wn$) to (CO$_2$)$_6$, (CO$_2$)$_7$, (CO$_2$)$_9$, (CO$_2$)$_{10}$, (CO$_2$)$_{11}$, (CO$_2$)$_{12}$, and (CO$_2$)$_{13}$. Spectra are obtained by direct absorption using a rapid-scan tuneable diode laser spectrometer to probe a pulsed supersonic slit-jet expansion and assignments are facilitated by recent calculations of Takeuchi based on the Murthy potential. \textbf{107}, 5703 (2008); C.S. Murthy, S.F. O'Shea, and I.R. McDonald, \textit{Mol. Phys.} \textbf{50}, 531 (1983).} (CO$_2$)$_6$ is a symmetric top with $S$$_6$ point group symmetry which can be thought of as a stack of two planar cyclic trimers. (CO$_2$)$_{13}$ is also an $S$$_6$ symmetric top, and consists of a single CO$_2$ monomer surrounded by an slightly distorted icosahedral cage. The remaining clusters are asymmetric tops without symmetry. Here we report additional CO$_2$ cluster results. Calculations based on the SAPT-s potential \textbf{110}, 3785 (1999).} indicate that the structure of (CO$_2$)$_{10}$ may be slightly different from that given by Takeuchi/Murthy. An additional band is observed for each of (CO$_2$)$_{13}$ and (CO$_2$)$_{10}$. A feature observed at 2378.2 $\wn$ is assigned as a (CO$_2$)$_6$ parallel combination band involving the sum of a fundamental and a low-lying intermolecular vibration. Most significantly, two bands are assigned to a second isomer of (CO$_2$)$_6$. This is also a symmetric top, but now with $S$$_4$ symmetry. The two symmetric hexamer isomers observed spectroscopically correspond well with the lowest energy structures given by both the SAPT-s and Murthy intermolecular potentials.
Description
Author Institution: Steacie Institute for Molecular Sciences, National Research; Council of Canada, Ottawa, ON K1A 0R6, Canada; Department of Physics and Astronomy, University of Calgary; 2500 University Dr., N.W., Calgary, AB T2N 1N4, Canada