Photoelectron angular distributions (PADs) from the liquid-water surface and from bulk liquid water are reported for water oxygen-1s ionization. Although less so than for the gas phase, the measured PADs from the liquid are remarkably anisotropic, even at electron kinetic energies lower than 100 eV, when elastic scattering cross sections for the outgoing electrons with other water molecules are large. The PADs reveal that theoretical estimates of the inelastic mean free path are likely too long at low kinetic energies, and hence the electron probing depth in water, near threshold ionization, appears to be considerably smaller than so far assumed.

A generalised liquid-phase photoelectron spectroscopy approach is reported, allowing accurate, absolute energy scale ionisation energies of liquid water and aqueous solutions, as well as liquid water's work function to be reported.

Identifying the initial products of the interaction of high-energy radiation with liquidwater is essential for understanding the yield and patterns of damage in aqueous condensed matter, including biological systems. Up until now several fast reactions induced by energetic particles in water could not be observed on their characteristic timescales, and hence some of the reaction intermediates involved, particularly those requiring nuclear motion, have not been considered in describing radiation chemistry.Here, through a combined experimental and theoretical study, we elucidate the ultrafast proton dynamics in the first few femtoseconds after X-ray core-level ionization of liquid water. We show through isotope analysis of the Auger-spectra that proton-transfer dynamics occurs on the same timescale as electron autoionization. Proton transfer leads to formation of a Zundel-type intermediate [HO*··H··OH 2 ] + , which further ionizes, forming a so-far unnoticed type of di-cationic, charge-separated species with high internal energy. We call the process proton-transfer mediated charge separation.The primary processes in water initiated by X-radiation are poorly understood despite their paramount importance in different fields. Understanding the energy and charge redistribution in water upon X-ray photon absorption is vital for a design of more efficient radio-oncology schemes, 1-2 for disentangling the physical basis of genotoxic effects on living tissues, [3][4][5] for minimizing the damage of biological samples during X-ray diffraction 2 experiments, 6 as well as for controlling the performance of nuclear reactors under operating conditions. 7 Current understanding of electron-initiated processes in aqueous systems, following energy deposition, and the subsequent radical chemistry have been recently reviewed. 8 An explicit consideration of radicals and molecular species formed via multiple ionization processes of water, involving for instance atomic oxygen and hydrogen peroxide, can be found in the radiolysis literature, e.g. in refs. 7,9 However, the knowledge of the ultrafast processes and mechanisms in water radiolysis remains to large extent unexplored.In the present work we focus on the processes following O1s core-level ionization of water. The highly excited species formed by the core ionization relaxes primarily via Augerelectron decay. As shown in Figure 1b, Auger decay of a water molecule involves refilling the water core-hole by one of the valence electrons, and the simultaneous emission of another valence electron, the Auger electron, from the same water molecule. The resulting highly reactive doubly ionized H 2 O 2+ (aq) molecule, with both vacancies (holes) located at the same site (denoted here as 2h state), then undergoes ultrafast Coulomb explosion, forming dominantly O + 2H + . [10][11] In recent years a set of novel non-local autoionization processes has been identified to play an important role in weakly bonded atomic and molecular systems. [12][13][14] One such relaxation process is Intermolecu...

Characterization of the structure and properties of matter would be incomplete without the detailed knowledge of electronic structure, and yet, for aqueous solutions, not even the binding energies of the valence electrons are generally known. Thus, fundamental interactions between solute electronic structure and water, essentially the key to chemical reactivity, have remained poorly understood. This work describes how, by the development of the vacuum liquid microjet technique for X-ray photoelectron spectroscopy, electronic structure measurements from aqueous solutions have advanced to date. Direct and resonant second-order electron emission processes are discussed in light of the specific electron structure information accessible from aqueous solutions. Several examples of solutes in their natural aqueous environment will be presented along with future research directions and prevailing challenges in the field.

Aqueous solutions of ferrous and ferric iron (Fe(2+/3+)) and of the iron-hexacyano complexes [Fe(CN)(6)](4-/3-) are studied by photoelectron spectroscopy using a liquid microjet in conjunction with synchrotron soft X-rays for ionization. For Fe(2+)(aq) we observe two well-resolved peaks at 7.09 and 9.16 eV electron binding energy (BE) that can be assigned to the iron-hexaaquo complex. For Fe(3+)(aq) we observe only one peak above the highest valence band of liquid water, at 10.08 eV BE. Interpreting the spectra in terms of the one-electron levels of Kohn-Sham density functional theory, we find that the two peaks for Fe(2+)(aq) originate from the energy splitting between the highest occupied β (= minority) spin level (Fe d(t(2g))) and the five highest occupied α (= majority) spin levels (Fe d(t(2g)) and d(e(g))). The peak for Fe(3+)(aq) arises from d-levels that are strongly mixed with the solvent. The spectra of the aqueous hexacyano complexes show a single strong peak at 6.11 and 7.52 eV BE for [Fe(CN)(6)](4-) and [Fe(CN)(6)](3-), respectively, originating from the highest occupied Fe d(t(2g)) levels, and two further peaks at higher BE originating from the cyano ligands. The PE spectra of the reduced aquo and cyano ions are then used to obtain-solely on experimental grounds-values for the reorganization free energy of the oxidized ions. DFT/continuum calculations of this important parameter in the Marcus theory of oxidation reactions are in fairly good agreement with experiment.

We report on the effects of electron collision and indirect ionization processes, occurring at photoexcitation and electron kinetic energies well below 30 eV on the photoemission spectra of liquid water....

Experimental studies of the electronic structure of excess electrons in liquids—archetypal quantum solutes—have been largely restricted to very dilute electron concentrations. We overcame this limitation by applying soft x-ray photoelectron spectroscopy to characterize excess electrons originating from steadily increasing amounts of alkali metals dissolved in refrigerated liquid ammonia microjets. As concentration rises, a narrow peak at ~2 electron volts, corresponding to vertical photodetachment of localized solvated electrons and dielectrons, transforms continuously into a band with a sharp Fermi edge accompanied by a plasmon peak, characteristic of delocalized metallic electrons. Through our experimental approach combined with ab initio calculations of localized electrons and dielectrons, we obtain a clear picture of the energetics and density of states of the ammoniated electrons over the gradual transition from dilute blue electrolytes to concentrated bronze metallic solutions.

L-edge soft X-ray spectroscopy has been proven to be a powerful tool to unravel the peculiarities of electronic structure of transition metal compounds in solution. However, the X-ray absorption spectrum is often probed in the total or partial fluorescence yield modes, what leads to inherent distortions with respect to the true transmission spectrum. In the present work, we combine photon- and electron-yield experimental techniques with multi-reference first principles calculations. Exemplified for the prototypical FeCl2 aqueous solution we demonstrate that the partial yield arising from the Fe3s → 2p relaxation is a more reliable probe of the absorption spectrum than the Fe3d → 2p one. For the bonding-relevant 3d → 2p channel we further provide the basis for the joint analysis of resonant photoelectron and inelastic X-ray scattering spectra. Establishing the common energy reference allows to assign both spectra using the complementary information provided through electron-out and photon-out events.