Resolving Nonadiabatic Dynamics of Hydrated Electrons Using Ultrafast Photoemission Anisotropy

We have studied ultrafast nonadiabatic dynamics of excess electrons trapped in the band gap of liquid water using time-and angle-resolved photoemission spectroscopy. Anisotropic photoemission from the first excited state was discovered, which enabled unambiguous identification of nonadiabatic transition to the ground state in 60 fs in H2O and 100 fs in D2O. The photoelectron kinetic energy distribution exhibited a rapid spectral shift in ca. 20 fs, which is ascribed to the librational response of a hydration shell to electronic excitation. Photoemission anisotropy indicates that the electron orbital in the excited state is depolarized in less than 40 fs.