Dipole-bound and interior electrons in water dimer and trimer anions: ab initio MO studies

Two types of structures of water dimer and trimer anions are found in the ab initio molecular orbital study with an extensively diffuse basis set. The first type is the dipole-bound anion, and the excess electron is distributed exteriorly, or on the surface of water clusters. In the second type of dimer and trimer anions, the excess electron is internally trapped between two waters. The electron correlation contributes to stabilizing the latter anions. The calculated vertical detachment energies for both types of trimers are positive.