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

Unlike benzene, 1,3,5,7-cyclooctatetraene (COT) is not an aromatic molecule and has a tub-like structure in its ground electronic state. However, coordination of Sc or Ti converts the tub-like structure into a planar ring structure. The M-COT (M = Sc, Ti) complexes formed by interactions of laser-vaporized metal atoms and the organic ligand are studied by pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy and density functional theory calculations. The theoretical calculations predict that both Sc/Sc+ and Ti/Ti+ prefer the eta8 binding with slightly different M-C distances. The resulting Sc/Sc+ and Ti+ complexes have C4v molecular symmetry, whereas Ti-COT has C2v symmetry, due to Jahn-Teller distortion. By comparing the experimental measurements and theoretical calculations, the photoelectron spectrum of the Sc complex is assigned to the 1A1 leftarrow 2A1 transition with a strong 0-0 transition at 42261(5) cm-1. On the other hand, the spectrum of the Ti complex is due to the transitions from two neutral states with similar energies, 3B1 and 3B2, to ionic 2A1 electronic state. These transitions display strong 0-0 transitions at 40887(5) and 40863(5) cm-1, respectively. In addition, a major vibrational progression (338 and 330 cm-1 for the Sc+- and Ti+-COT stretch frequencies, respectively) and a number of vibrational hot bands are observed for the two complexes.