With ab initio molecular orbital calculations, the structures of the cation clusters Mg+(H20)" and their hydrogen-eliminated products (Mg0H)+(H20)"-i are optimized. In Mg+(H20)", the hydration number of the most stable isomer is 3. In (Mg0H)+(H20)"-i, all water molecules are directly bonded to Mg+ for n < 6. The hydration energy of (MgOH)+ is larger than that of Mg+ because of the strongly polarized (MgOH)+ molecular ion; Mg is oxidized halfway to Mg(II). The internal energy change of the hydrogen elimination of Mg+(H20)" is positive for n = 1-5, but becomes negative for n = 6, which is in good agreement with the product switching in the TOF spectrum reported in the preceding paper by Sanekata et al. The effects of isotope substitution and equilibrium constants of the hydrogen (deuterium) elimination reaction observed in their experiment can be explained qualitatively.

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Photoelectron spectra (PESs) of Li-(NH3) n (n ≤ 16), Na-(NH3) n (n ≤ 12), and Na-(H2O) n (n ≤ 7), as well as the ionization potentials (IPs) of Li(NH3) n (n ≤ 28) and Li(H2O) n (n ≤ 46), are examined. PESs of Li-(NH3) n (n ≤ 10) exhibit three bands derived from the Li(32S)−Li-(1S), Li(22P)−Li-(1S), and Li(22S)−Li-(1S) transitions. The vertical detachment energies of the 32S- and 22P-type states decrease dramatically with increasing n. For n ≥ 11, the transitions to the 22P- and 32S-type states almost become degenerate with the transition of the neutral ground (22S) state. In addition to these observations, we also find the red shift of the 22S-type transition with a much slower rate. The similar spectral trends are also observed for the Na(32P)−Na-(1S) and Na(32S)−Na-(1S) transitions of Na-(NH3) n . On the other hand, the transitions of Na-(H2O) n exhibit the opposite shifts, and the 2P−2S energy separation does not change. As for Li(H2O) n , we find a monotonous decrease in IPs with n ≤ 4 and a constant IP behavior for n ≥ 5. The limiting value for n → ∞ (3.12 eV) is comparable to the estimated photoelectric threshold of ice as in the case of Cs(H2O) n reported previously. On the basis of these results as well as those of the ab initio calculations, we discuss the early stage of solvated-electron formation in finite clusters.