Excess electrons in polar cluster anions

Different mechanisms are involved in thermal electron attachment to assemblies of closed-shell polar molecules. Dipole-bound anions can be created from small clusters with total resultant dipole moments that are larger than a critical value of 2.5 D. The cluster anion excess electrons are in very diffuse orbitals located outside the molecular frame. Anions and their neutral parents then have the same geometrical structures. The electron binding energies are very small and external electric fields can easily detach the excess electrons. Excess electrons can be localized in valence orbitals of closed-shell polar molecules with dipole moments smaller than 2.5 D if these molecules are imbedded in small nonhomogeneous clusters. Solvation effects then lead to the formation 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.