Time-resolved observation of the Eigen cation in liquid water

Experimental observation and time relaxation measurement of the hydrated proton Eigen form [H3O+(H2O)3] are presented here. Vibrational time-resolved spectroscopy is used with an original method of investigating the proton excess in water. The anharmonicity of the time-resolved spectra is characteristic of the Eigen-type proton geometry. Proton relaxation occurs in less than 200fs. A calculation of the potential energy confirms the experimental result and the Eigen cation lifetime is in good agreement with previous molecular dynamics simulations.