15min:

RUCHIRA SILVA AND DONG-SHENG YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

Slow electron velocity-map imaging (SEVI) was used to study the structures and electronic states of La₂(C₆H₆) and La(C₆H₆)₂ complexes formed in a metal cluster beam source. Electron spectra obtained from SEVI have the energy resolution of E/eKE ~ 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 La₂(C₆H₆) and 39033(5) cm^-1 for La(C₆H₆)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 [La₂(C₆H₆)]⁺ and 408 cm^-1 for [La(C₆H₆)₂]⁺. By combining the spectra with theoretical calculations, we identified the ²A_g ¹A_g transition of La₂(C₆H₆) (C_2h) and ³A ²A of La(C₆H₆)₂ (C₁). By measuring the anisotropy parameter ( ) from photoelectron angular distribution, we found that the outgoing electron was from a largely La 6s-based molecular orbital in both complexes.