The streaming potentials of liquid beams of aqueous NaCl, NaBr, and NaI solutions are measured using soft X-ray, He(I), and laser multiphoton ionization photoelectron spectroscopy. Gaseous molecules are ionized in the vicinity of liquid beams and the photoelectron energy shifts are measured as a function of the distance between the ionization point and the liquid beam. The streaming potentials change their polarity with concentration of electrolytes, from which the singular points of concentration eliminating the streaming potentials are determined. The streaming currents measured in air also vanish at these concentrations. The electron binding energies of liquid water and I(-), Br(-), and Cl(-) anions are revisited and determined more accurately than in previous studies.

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High-resolution soft X-ray photoelectron spectra of liquid water (H(2)O and D(2)O) were measured using a liquid beam photoelectron spectrometer. The 1a(1) (O1s) band and the lowest valence 1b(1) band had single peaks, which is not consistent with the split 1b(1)→ 1a(1) of the X-ray emission band of liquid water if the splitting is assumed to originate from level shifts in two different hydrogen bonding structures. The second valence 3a(1) band of liquid water exhibited a flat top implying that two bands exist underneath a broad feature, which is similar to the case of the 3a(1) band of amorphous ice. The energy splitting between the two 3a(1) bands is estimated to be 1.38 eV (H(2)O) and 1.39 eV (D(2)O). Ab initio calculations suggest that the large splitting of the 3a(1) band is characteristic of water molecules that function as both proton donor and acceptor. The overall result is consistent with the conventional model of a tetrahedral hydrogen-bonding network in liquid water.

Interatomic Coulombic decay (ICD) from an Auger-final dicationic state is observed in the Ar dimer. A 2p inner-shell vacancy created by photoionization is replaced with 3s and 3p vacancies via intra-atomic Auger decay. The Auger-final dicationic state is subject to ICD in which one of the 3p electrons in the same Ar atom fills the 3s vacancy while one of the 3p electrons from the neighboring Ar atom is emitted as an ICD electron. This ICD process is unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ICD electron and the kinetic energy release between Ar+ and Ar2+ are measured in coincidence.

Time-resolved hard x-ray photoelectron spectroscopy (trHAXPES) is established using the x-ray free-electron laser SACLA. The technique extends timeresolved photoemission into the hard x-ray regime and, as a core-level spectroscopy, combines element and atomic-site specificity and sensitivity to the chemical environment with femtosecond time resolution and bulk (sub-surface) sensitivity. The viability of trHAXPES using 8 keV x-ray free-electron-laser radiation is demonstrated by a systematic investigation of probe and pump pulseinduced vacuum space-charge effects on the V 1s emission of VO 2 and the Ti 1s emission of SrTiO 3 . The time and excitation energy dependencies of the measured spectral shifts and broadenings are compared to the results of N-body numerical simulations and simple analytic (mean-field) models. Good agreement between the experimental and calculated results is obtained. In particular, the 9 Present address: characteristic temporal evolution of the pump pulse-induced spectral shift is shown to provide an effective means to determine the temporal overlap of pump and probe pulses. trHAXPES opens a new avenue in the study of ultrafast atomic-site specific electron and chemical dynamics in materials and at buried interfaces.Keywords: time-resolved photoelectron spectroscopy, x-ray free-electron laser, space-charge effects IntroductionSub-picosecond time-resolved solid-state photoemission spectroscopy has recently emerged as a powerful novel technique for studying the electronic properties of condensed matter. The power of the technique is that it provides direct access to the electronic structure dynamics in materials and at their surfaces on the time scales of the underlying elementary electronic and lattice processes, such as electron-electron scattering, electron screening and thermalization, coherent phonon vibrations, electron-phonon and phonon-phonon coupling, as well as substrate-adsorbate charge transfer or the buildup of surface photovoltages. Time-resolved photoemission spectroscopy generally combines frequency-domain information with subpicosecond time resolution through a pump-probe scheme in which typically an infrared (IR) pump pulse is used to excite the system whose dynamics is then probed at different time delays by detecting the photoelectrons emitted by ultrashort pulses in the ultraviolet (UV) to soft x-ray regime. When probe pulses in the UV to extreme ultraviolet (XUV) range are used and angular resolution is added, the technique is referred to as time-and angle-resolved photoemission spectroscopy (trARPES) and provides direct information on the momentum-resolved dynamics of valence electrons, including the temporal evolution of electronic populations, band structures, Fermi surfaces, and energy gaps [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. When the probe pulses have higher photon energies, in the extreme ultraviolet to soft x-ray range, the technique becomes time-resolved x-ray photoemission spectroscopy (trXPS), with element specificity, sensitivi...