PULSED FIELD IONIZATION ELECTRON SPECTROSCOPY OF CYCLOPENTADIENYL DIALUMINUM COMPLEX
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Date
2006
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Ohio State University
Abstract
The cyclopentadienyl dialuminum complex, (C$_{5}$H$_{5}$)Al$_{2}$, is synthesized in a supersonic molecular beam, where aluminum atoms and dimers are produced by laser vaporization, and cyclopentadienyl radicals are generated from photolysis of cyclopentadiene (C$_{5}$H$_{6}$) molecules. Vibrationally resolved electronic spectra of the complex are measured using pulsed-field ionization zero electron kinetic energy spectroscopy. Three initial conformations are considered for the complex: one with an Al atom binding to each side of the C$_{5}$H$_{5}$ ring and two others with an Al$_{2}$ molecule lying vertically or horizontally on one side of the ligand ring. A structure with the Al$_{2}$ molecule lying vertically on the top of the C$_{5}$H$_{5}$ ring is identified by comparing the spectroscopic measurements to $ab$ $initio$ calculations. The (C$_{5}$H$_{5}$)Al$_{2}$ neutral complex has a $^2$A$^{\prime \prime}$ ground electronic state in Jahn-Teller distorted $C$$_{s}$ symmetry and the corresponding ion has a $^1$A$_1$ ground state in $C$$_{5v}$ symmetry. The ionization energy of (C$_{5}$H$_{5}$)Al$_{2}$ is measured to be 40690(5) cm$^{-1}$. For the cationic $^1$A$_1$ state, the frequencies of the metal-ligand stretching, metal-metal stretching, and metal-ligand bending modes are 482, 175, and 50 cm$^{-1}$, respectively. In addition, a (C$_{5}$H$_{5}$)-Al$_{2}$ bending mode of the neutral $^2$A$^{\prime \prime}$ state is measured to be 26 cm$^{-1}$.
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Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055