Metastable decay of photoionized niobium clusters: Clusters within a cluster?

Abstract

The photoinduced metastable ion fragmentation of niobium clusters has been found to closely correlate with the laser vaporization source conditions. The experimental evidence indicates the clusters agglomerate in the supersonic expansion. These agglomerated clusters exhibit rather unique behavior for a transition metal system. Both evaporation and fission fragmentation are observed. Two color MPI studies reveal the existence of long lived neutral intermediate states. Also, the kinetic energy release is extremely small, <10 meV, and independent of the excitation energy. The concept of clusters within a cluster, i.e., agglomerated clusters, is introduced to rationalize many experimental findings.