The shape of small metal clusters is determined by forces intermediate between those of the isolated molecule and the extended solid. Particle shape plays an important role in surface interactions and catalytic behavior. This project will apply microwave-optical double resonance spectroscopy to determine the nature and extent of Jahn-Teller distortions in the vibronic spectra of small metal clusters. These experimental measurements will be a rigorous benchmark against which present theoretical calculations will be evaluated. This project is jointly supported by the Physics and Chemistry Divisions of NSF.