Communications: Observation of two classes of isomers of hydrated electrons in sodium-water clusters.

A new class of sodium-water clusters with a low lying ionization potential (IP) is characterized by their photoionization spectra in molecular beam experiments. This implies that Na(H(2)O)(n) clusters coexist for n>or=15 in two forms of significant abundances being distinguished by their IPs of approximately 2.8 and approximately 3.2 eV. A tentative quantum chemical characterization was achieved by simulating ionization spectra for selected cluster sizes using an ab initio molecular dynamics approach. Experiment and theory suggest that the Na(+)-e(-) distance is significantly larger in the clusters with the lower IP. This indicates that the solvated electron in Na(H(2)O)(n) clusters very probably forms with the Na(+) counterion both a solvent separated and a contact ion pair.