EXCESS ELECTRONS IN POLAR CLUSTER ANIONS

Different mechanisms are involved in thermal electron attachment to as semblies of closed-shell polar molecules. Dipole-bound anions can be c reated from small clusters with total resultant dipole moments that ar e larger than a critical value of 2.5 D. The cluster anion excess elec trons are in very diffuse orbitals located outside the molecular frame . Anions and their neutral parents then have the same geometrical stru ctures. The electron binding energies are very small and external elec tric fields can easily detach the excess electrons. Excess electrons c an be localized in valence orbitals of closed-shell polar molecules wi th dipole moments smaller than 2.5 D if these molecules are imbedded i n small nonhomogeneous clusters. Solvation effects then lead to the fo rmation of covalent anions. Excess electrons can also be collectively bound by large polar clusters and the corresponding anions are similar to solvated electrons in liquids.