Abstract

We have studied the production of neutral metastable fragments in electron collisions with neutral argon clusters. The fragments are detected using a time-of-flight technique. The time-of-flight spectra show that the metastable fragments appear in two velocity ranges. Kinetic energy distributions are obtained, showing that the faster fragments are ejected with energies from 0.2 to 1.5 eV and that the slower fragments have energies less than 0.2 eV. It is argued that the fragmentation of the clusters involves the excitation and decay of excitons in the clusters.The faster fragments are produced by n52 excitons, which localize on an excimer or an excited trimer within the cluster and upon dissociation cause the ejection of a metastable atom. The slower fragments are produced by n51 excitons, which tend to localize on the periphery of the cluster, leading to the ejection of a metastable atom due to weak repulsive forces with neighboring atoms. Four different production mechanisms for neutral metastable fragments are observed.