The ground and low-lying excited states of Na(NH3)(n) and Na((HO)-O-2)(n) (n = 1-8) clusters were studied using ab initio molecular orbital methods. The calculated vertical transition energies to the 3(2)P(Na)-type states agree well with the energies of the absorption maxima. The clusters change from a valence state to a two-center state via a diffuse one-center state with increasing n in both the ground and excited states. The localization of an unpaired electron proceeds at a faster rate against n in Na(H2O)(n) than in Na(NH3)(n). The formation of an excited state of the solvated electron is found in Na(H2O)(4-8). (C) 2008 Elsevier B. V. All rights reserved.