Probing the Structural Evolution of the Hydrated Electron in Water Cluster Anions (H_2O)_n~-, n ≤ 200, by Electronic Absorption Spectroscopy

摘要

Electronic absorption spectra of water cluster anions (H2O)(n)(-), n <= 200, at T = 80 K are obtained by photodissociation spectroscopy and compared with simulations from literature and experimental data for bulk hydrated electrons. Two almost isoenergetic electron binding motifs are seen for cluster sizes 20 <= n <= 40, which are assigned to surface and partially embedded isomers. With increasing cluster size, the surface isomer becomes less populated, and for n >= 50, the partially embedded isomer prevails. The absorption shifts to the blue, reaching a plateau at n approximate to 100. In this size range, the absorption spectrum is similar to that of the bulk hydrated electron but is slightly red-shifted; spectral moment analysis indicates that these clusters are reasonable model systems for hydrated electrons near the liquid-vacuum interface.