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► Ultrafast charge transfer in aqueous electrolytes is observed in Auger spectroscopy. ► Delocalization time-scales for various cations, anions and water are probed. ► The influence ...of both the magnitude, sign of charge and size of ions is discussed. ► Future directions for studying ultrafast charge-transfer processes are identified.
We review the basic principles of ultrafast charge delocalization phenomena in aqueous electrolytes following core-level photoionization and resonant core-level excitations, and describe how these processes can be probed using Auger electron spectroscopy. The use of the core–hole clock method to extract dynamical information from Auger spectra is described. By a number of examples we demonstrate how the efficiency for ultrafast charge transfer phenomena on the low femtosecond timescale is determined not only by factors such as charge, polarizability and solvated radius of the ionic solutes but also by the dominant interactions of the ionized site with its surroundings in the intermediate state.
Correction for 'The molecular structure of the surface of water-ethanol mixtures' by Johannes Kirschner
et al.
,
Phys. Chem. Chem. Phys.
, 2021,
23
, 11568-11578, DOI:
10.1039/D0CP06387H
.
Effect of Cations on the Hydrated Proton Ottosson, Niklas; Hunger, Johannes; Bakker, Huib. J
Journal of the American Chemical Society,
09/2014, Letnik:
136, Številka:
37
Journal Article
Recenzirano
We report on a strong nonadditive effect of protons and other cations on the structural dynamics of liquid water, which is revealed using dielectric relaxation spectroscopy in the frequency range of ...1–50 GHz. For pure acid solutions, protons are known to have a strong structuring effect on water, leading to a pronounced decrease of the dielectric response. We observe that this structuring is reduced when protons are cosolvated with salts. This reduction is exclusively observed for combinations of protons with other ions; for all studied solutions of cosolvated salts, the effect on the structural dynamics of water is observed to be purely additive, even up to high concentrations. We derive an empirical model that quantitatively describes the nonadditive effect of cosolvated protons and cations. We argue that the effect can be explained from the special character of the proton in water and that Coulomb fields exerted by other cations, in particular doubly charged cations like Mg2+ aq and Ca2+ aq, induce a localization of the H+ aq hydration structures.
Starting a business is one way out of unemployment for many people. Having a small pool of job applicants may, however, affect the quality of manpower available to employers. This paper reports the ...results of an experimental study that examined whether job-seekers discriminate against prospective employers based on those employers' ethnicity and sex. We conducted an experiment with 889 university students, where we presented 10 hypothetical job vacancies in the restaurant sector to the participants. We then asked participants to state their willingness to apply to each job. The ethnicity and sex of the employers were conveyed through employers' names by using typical male and female Arabic- and Swedish-sounding names. Overall, our results provided no evidence of ethnic or sex discrimination by job-seekers against employers.
The acid–base speciation of surface-active carboxylate ions in the surface region of aqueous solutions was studied with synchrotron-radiation-based photoelectron spectroscopy. The protonated form was ...found at an extraordinarily large fraction compared to that expected from the bulk pH. When adding salts containing the weak acid NH4 + to the solution, the fraction of the acidic form at the surface increases, and to a much greater extent than expected from the bulk pH of the solution. We show that ammonium ions also are overrepresented in the surface region, and propose that the interaction between the surface-active anionic carboxylates and cationic ammonium ions creates a carboxylate-ammonium bilayer close to the surface, which increases the probability of the protonation of the carboxylate ions. By comparing the situation when a salt of the less volatile amine diethanolamine is used, we also show that the observed evaporation of ammonia that occurs after such an event only affects the equilibrium marginally.
Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are ...characterized. The fact that the N 1s binding energies differ between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range, and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed solutions can be explained by replacement of ammonium ions by guanidinium ions in the surface region in combination with a strong salting-out effect of guanidinium by ammonium ions at increased concentrations. This interpretation is supported by molecular dynamics simulations, which reproduce the experimental trends very well. The simulations suggest that the relatively higher surface propensity of guanidinium compared with ammonium ions is due to the ease of dehydration of the faces of the almost planar guanidinium ion, which allows it to approach the water-vapor interface oriented parallel to it.
The molecular and electronic structures of aqueous I3(-) and I(-) ions have been investigated through ab initio molecular dynamics (MD) simulations and photoelectron (PE) spectroscopy of the iodine ...4d core levels. Against the background of the theoretical simulations, data from our I4d PE measurements are shown to contain evidence of coupled solute-solvent dynamics. The MD simulations reveal large amplitude fluctuations in the I-I distances, which couple to the collective rearrangement of the hydrogen bonding network around the I3(-) ion. Due to the high polarizability of the I3(-) ion, the asymmetric I-I vibration reaches partially dissociated configurations, for which the electronic structure resembles that of I2 + I(-). The charge localization in the I3(-) ion is found to be moderated by hydrogen-bonding. As seen in the PE spectrum, these soft molecular vibrations are important for the electronic properties of the I3(-) ion in solution and may play an important role in its electrochemical function.
The photoelectron spectra of aqueous imidazole are presented, and the N 1s and C 1s binding energies are assigned aided by density functional theory calculations. The chemical equivalency of the two ...nitrogens of the cationic form is directly identified by the occurrence of a single N 1s photoelectron peak, which results from the delocalization of the positive charge over the molecule as a consequence of the Cv symmetry of the system. In contrast to NMR measurements, the photoemission process is faster than the rapid proton exchange in the aqueous environment, making the pseudoequivalent nitrogens of the neutral state clearly distinguishable with a N 1s binding energy shift of 1.7 eV.
Auger electron spectroscopy combined with theoretical calculations has been applied to investigate the decay of the Ca 2p core hole of aqueous Ca(2+). Beyond the localized two-hole final states on ...the calcium ion, originating from a normal Auger process, we have further identified the final states delocalized between the calcium ion and its water surroundings and produced by core level intermolecular Coulombic decay (ICD) processes. By applying the core-hole clock method, the time scale of the core level ICD was determined to be 33 +/- 1 fs for the 2p core hole of the aqueous Ca(2+). The comparison of this time constant to those associated with the aqueous K(+), Na(+), Mg(2+), and Al(3+) ions reveals differences of 1 and up to 2 orders of magnitude. Such large variations in the characteristic time scales of the core level ICD processes is qualitatively explained by different internal decay mechanisms in different ions as well as by different ion solvent distances and interactions.
The molecular and electronic structures of aqueous I-3 and I ions have been investigated through ab initio molecular dynamics (MD) simulations and photoelectron (PE) spectroscopy of the iodine 4d ...core levels. Against the background of the theoretical simulations, data from our I4d PE measurements are shown to contain evidence of coupled solute-solvent dynamics. The MD simulations reveal large amplitude fluctuations in the I-I distances, which couple to the collective rearrangement of the hydrogen bonding network around the I-3(-) ion. Due to the high polarizability of the I-3(-) ion, the asymmetric I-I vibration reaches partially dissociated configurations, for which the electronic structure resembles that of I-2 + I-. The charge localization in the I-3(-) ion is found to be moderated by hydrogen-bonding. As seen in the PE spectrum, these soft molecular vibrations are important for the electronic properties of the I-3(-) ion in solution and may play an important role in its electrochemical function.
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