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 ${\mathrm{H}}_2\mathrm{O}$ and 100 fs in ${\mathrm{D}}_2\mathrm{O}$. 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.

• Received 21 June 2015

DOI:https://doi.org/10.1103/PhysRevLett.116.137601