Neutral sodium-water clusters are formed in a "pickup" source, injection of a beam of Na atoms into the expansion zone of a pulsed nozzle-jet beam of water vapor seeded into an argon carrier gas. They are detected by near-uv one-photon ionization with a pulsed laser and time-of-flight mass spectroscopy. NaCHaO^-cluster-ion signals up to n = l2 are seen, « = 4 showing a very pronounced abundance. The ionization potential of NaOHa is determined to be 4.379 ±0.002 eV.

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The lowest electronically excited state of small Na(H 2 O) n clusters have been investigated experimentally and theoretically. The excitation energy as determined by the depletion spectroscopy method drops from 16950 cm −1 for the sodium atom down to 9670 cm −1 when only three water molecules are attached to the Na atom. For larger clusters the absorption band shifts back towards higher energies and reaches 10880 cm −1 for n = 12. The experimental data are compared to quantum chemical calculations at the MP2 and MRSDCI levels. We found that the observed size-dependence of the transition energy is well reproduced by the interior structure where the sodium atom is surrounded by water molecules. The analysis of the radial charge distribution of the unpaired electron in these interior structures gives a new insight into the formation of the "solvated" electron.