15min:
PHOTOELECTRON AND PHOTOION SPECTROSCOPY OF SCANDIUM-METHYLBENZENE COMPLEXES.

JUNG SUP LEE, YUXIU LEI, SUDESH KUMARI AND DONG-SHENG YANG, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

We report here single UV photon pulsed field ionization-zero electron kinetic energy (PFI-ZEKE) photoelectron spectra of jet-cooled Sc-[C6H6-n(CH3)n] (n = 2, 3, and 6) complexes and two-photon IR-UV photoionization spectra of Sc-[C6(CH3)6]. Adiabatic ionization energies and low-frequency metal-ligand and ligand-based vibrational modes are measured from the single-photon PFI-ZEKE spectra, and C-H stretching frequencies are determined from the two-photon IR-UV spectra. The ionization energies of these Sc complexes decrease with increasing methyl substations of hydrogen in the benzene ring. The C-H frequencies of hexamethylbenzene are significantly shifted due to Sc coordination. The ZEKE transitions of the di- and tri-methyl substituted complexes are sharp, while those of the hexa-methyl species are rather broad. The observed electronic transitions are 1A leftarrow 2A for Sc-[1,4-C6H4(CH3)2] (C2), 1A' leftarrow 2A' for Sc-[1,3,5-C6H3(CH3)3] (Cs), and 1A1 leftarrow 2A1 for Sc-[C6(CH3)6] (C2v).