Infrared photodissociation spectroscopy of metal benzene cation complexes
Reishus, Kimberly Nicole
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Singly charged metal-benzene cation complexes are made using a laser vaporization source in a pulsed supersonic expansion. The infrared spectra of mass selected Al+(bz)1-4 and Co+(bz)1-3 ions is measured using photodissociation spectroscopy and rare gas tagging. Density functional theory is used to calculated the structures, binding energies, and vibrational spectra of these complexes. Spectra of Al+(bz)1-4 in the C-H stretch region show a sharp multiplet pattern known as the Fermi triad of free benzene. In the fingerprint region strong vibrations were detected and assigned to the ν11 out-of-plane hydrogen band and ν19 C-C ring motion. The ν11 band is strongly blue shifted from the free benzene vibration, and the ν19 band is slightly red shifted. Computed structures indicate a coordination of three benzene ligands around the metal cation. Preliminary spectra of Co+(bz)1-2 in the C-H stretch region show a single, broad band, whereas the Co+(bz)3 spectrum shows a quartet corresponding to the Fermi triad and a red-shifted C-H stretch. In the fingerprint region of Co+(bz)2 a doublet is assigned to the ν19 band, indicating the benzene ligands are distorted. The calculated structures indicate Co+(bz)2 has a spin multiplicity of one, but more results are needed before any conclusions are final.