The work to be performed in this program is the spectroscopy of alkali clusters at the rotational level using resonant two-photon ionization and optical-optical double resonance spectroscopy. The goal of the experiments is to probe the dynamic behavior of the vibronic states through the influence of ro-vibronic coupling on the rotational levels. Clusters form the bridge between gas phase atomic physics and condensed matter physics, and the information which is sought at this detailed level is fundamental to understanding the transition from one phase to the next.