SLOW ELECTRON VELOCITY-MAP IMAGING OF La$_2$(C$_6$H$_6$) AND La(C$_6$H$_6$)$_2$
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Date
2013
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Ohio State University
Abstract
Slow electron velocity-map imaging (SEVI) was used to study the structures and electronic states of La$_2$(C$_6$H$_6$) and La(C$_6$H$_6$)$_2$ complexes formed in a metal cluster beam source. Electron spectra obtained from SEVI have the energy resolution of $\Delta$E/eKE $\approx$ 2$\%$ at eKE=400cm$^{-1}$. The SEVI technique offers much higher data collection efficiency than pulsed-field ionization zero electron kinetic energy spectroscopy. From the SEVI spectra, adiabatic ionization energies were measured to be 32141(5) cm$^{-1}$ for La$_2$(C$_6$H$_6$) and 39033(5) cm$^{-1}$ for La(C$_6$H$_6$)$_2$. The most active vibrational transition for both complexes was identified to be a metal-ligand stretching mode with a frequency of 180 cm$^{-1}$ in the ion state. In addition, a benzene ring out-of-plane deformation mode was measured to be 303 cm$^{-1}$ for [La$_2$(C$_6$H$_6$)]$^+$ and 408 cm$^{-1}$ for [La(C$_6$H$_6$)$_2$]$^+$. By combining the spectra with theoretical calculations, we identified the $^2$A$_g$$\leftarrow$$^1$A$_g$ transition of La$_2$(C$_6$H$_6$) (C$_{2h}$) and $^3$A$\leftarrow$$^2$A of La(C$_6$H$_6$)$_2$ (C$_1$). By measuring the anisotropy parameter ($\beta$) from photoelectron angular distribution, we found that the outgoing electron was from a largely La 6s-based molecular orbital in both complexes.
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Author Institution: Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055