Full valence band photoemission from liquid water using EUV synchrotron radiation

The valence band photoelectron spectra of liquid water (H2O and D2O) are studied in the photon energy range from hv = 60 to 120 eV. The experiments use a 6 mum diameter liquid-jet free vacuum surface at the MBI undulator beamline of the synchrotron radiation facility BESSY. Photoelectron emission from all four valence molecular orbitals (MOs) is observed. In comparison to those of the gas phase, the peaks are significantly broadened and shifted to lower binding energies by about 1.5 eV. This is attributed primarily to the electronic polarization of the solvent molecules around an ionized water molecule. Energy shifts, peak broadening, and relative peak intensities for the four MOs differ because of their specific participation in the hydrogen bonding in liquid water. Relative photoionization cross sections for MOs were measured for hv = 60, 80, and 100 eV. The main difference for liquid water, as compared to the gas phase, is the relative intensity decrease of the 1b(2) and 3a(1) orbitals, reflecting changes of the MOs due to H-bonding.