Role of alkali cations for the excited state dynamics of liquid water near the surface.

Time-resolved liquid jet photoelectron spectroscopy was used to explore the excited state dynamics at the liquid water surface in the presence of alkali cations. The data were evaluated with the help of ab initio calculations on alkali-water clusters and an extension of these results on the basis of the dielectric continuum model: 160 nm, sub-20 fs vacuum ultraviolet pulses excite water molecules in the solvent shell of Na(+) or K(+) cations and evolve into a transient hydrated complex of alkali-ion and electron. The vertical ionization energy of this transient is about 2.5 eV, significantly smaller than that of the solvated electron.