| Abstract | Thirteen specific infrared bands in the 2350 cm -1 region are assigned to carbon dioxide clusters, (CO 2) N, with N = 6, 7, 9, 10, 11, 12 and 13. The spectra are observed in direct absorption using a tuneable infrared laser to probe a pulsed supersonic jet expansion of a dilute mixture of CO 2 in He carrier gas. Assignments are aided by cluster structure calculations made using two reliable CO 2 intermolecular potential functions. For (CO 2) 6, two highly symmetric isomers are observed, one with S 6 symmetry (probably the more stable form), and the other with S 4 symmetry. (CO 2) 13 is also symmetric (S 6), but the remaining clusters are asymmetric tops with no symmetry elements. The observed rotational constants tend to be slightly (≈2%) smaller than those from the predicted structures. The bands have increasing vibrational blueshifts with increasing cluster size, similar to those predicted by the resonant dipole-dipole interaction model but significantly larger in magnitude. © 2011 American Institute of Physics. |
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