Abstract

In recent years clusters and in particular metal clusters have been the fascinating subject of many experimental and theoretical studies. Cluster physics bridge the gap between molecular physics and solid state physics. Metal clusters exhibit distinct features ranging from molecular properties seen in small particles to solid state like behaviour of large aggregates. We report cluster size dependent studies of physical and chemical properties such as absorption resonances, lifetimes, decay channels and ionisation processes of the one- and two electron metal clusters Na_n and Hg_n. For these studies we introduced a new experimental technique consisting of the combination of a cluster beam, ion- and electron spectroscopy and tunable femtosecond laser pump-probe techniques. A major result of our femtosecond experiments is that the conventional view of the optical response of metal cluster, e.g. absorption, ionisation and decay processes as well as the relevant time scale, had to be changed. Our results clearly show that for Na_n and cluster sizes n≤21 molecular structure, excitations and properties prevail over collective excitations and surface plasmon-like properties.

© 1994 Optical Society of America