Stability, evaporation, and temperature of metal clusters

The stabilities of free metal clusters in beams, as well as their physical and chemical properties, are governed by the shell structure of the quantiz ed electronic levels. In addition, the properties of a cluster depend upon its internal thermal energy, or temperature. We describe a new method to de termine the temperature of free neutral clusters. Laser-induced photodissoc iation of sodium clusters is used to measure the recoil pattern of fragment ation products and thereby the amount of kinetic energy release. The fragme ntation profess is treated by an evaporation model similar to the statistic al theory of the disintegration of compound nuclei. From the kinetic energi es of evaporation, we determine the temperatures of both the daughter and t he mother particles. (C) 1999 Elsevier Science B.V. All rights reserved.