Hydration process of Na2- in small water clusters: photoelectron spectroscopy and theoretical study of Na2- (H2O)n.

Photoelectron spectroscopy (PES) of Na 2 - (H 2 O) n (n ≤ 6) was investigated to examine the solvation of sodium aggregates in small water clusters. The PES bands for the transitions from the anion to the neutral ground and first excited states derived from Na 2 (1 1 Σg + ) and Na 2 (1 3 Σ u + ) shifted gradually to the blue, and those to the higher-excited states correlated to the 3 2 S + 3 2 P asymptote dropped down rapidly to the red and almost degenerated on the 1 3 Σ u + -type band at n = 4. Quantum chemical calculations for n up to 3 showed that the spectra can be ascribed to structures where one of the Na atoms is selectively hydrated. From the electron distributions, it is found that the Na - -Na+(H 2 O) n - -type electronic state grows with increasing cluster size, which can be regarded as a sign of the solvation of Na 2 - with ionization of the hydrated Na.