15min:

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

The cyclopentadienyl dialuminum complex, (C₅H₅)Al₂, 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 (C₅H₆) 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 C₅H₅ ring and two others with an Al₂ molecule lying vertically or horizontally on one side of the ligand ring. A structure with the Al₂ molecule lying vertically on the top of the C₅H₅ ring is identified by comparing the spectroscopic measurements to ab initio calculations. The (C₅H₅)Al₂ neutral complex has a ²A'' ground electronic state in Jahn-Teller distorted C_s symmetry and the corresponding ion has a ¹A₁ ground state in C_5v symmetry. The ionization energy of (C₅H₅)Al₂ is measured to be 40690(5) cm^-1. For the cationic ¹A₁ 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 (C₅H₅)-Al₂ bending mode of the neutral ²A'' state is measured to be 26 cm^-1.