Photothermodissociation of selenium clusters

The dissociation of selenium cluster ions containing from 7 up to 30 atoms has been studied using unimolecular decay of photothermoexcited clusters. Clusters containing more than 14 atoms evaporate Se-6, Se-7, and Se-8 species, whereas smaller clusters with 7-10 atoms dissociate manly by Se-2 loss. When the size increases, Se-6 becomes the predominant channel showing a dissociation which evolves toward the bulk behavior. The changes in the observed channels correlate to changes in the dissociation energies which are deduced from the measured fractional dissociation rates and from the entropy contribution. Together with the previous study of tellurium clusters, this work provides comparative behavior of dissociation energies of group VI clusters and their convergence toward bulk properties. (C) 2000 American Institute of Physics. [S0021-9606(00)00223-3].