LiquidJet PES: Soft X-ray Photoelectron Spectroscopy from Aqueous Solution end-station at BESSY II

The LiquidJet PES apparatus is a specialized end-station at the synchrotron radiation facility BESSY II, Berlin, for studying the electronic structure of liquid water, aqueous and non-aqueous solutions with soft X-ray photoelectron spectroscopy. Targets are liquid microjets that are introduced into a vacuum chamber via a ~20 µm glass capillary

In-situ X-ray spectroscopy of the electric double layer around TiO2 nanoparticles dispersed in aqueous solution: Implications for H2 generation

We report an experimental observation of a significant amount of hydroxide (OH–) created upon water dissociation and subsequently trapped around TiO2 nanoparticles dispersed in NH4OH aqueous solution. The hydroxide species is identified and quantified by a combination of photoemission and photon emission X-ray spectroscopies conducted on liquid samples using a liquid microjet. Unlike previous X-ray studies that observed only a few monolayers of water coverage on TiO2 surfaces and found maximally submonolayer of OH–, the true aqueous environment adopted in this study enables ion mobility and the separation of the water dissociation products H+/OH–. This facilitates the formation of OH– diffused multilayer in which the trapped OH– ions are discovered to coordinate with three water molecules to form a tetrahedral hydration configuration. The negatively charged diffuse layers, together with the positive NH4+ Stern layers, constitute >0.8 nm thick electric double layers around the TiO2 nanoparticles. The large observed amount of hydroxide indicates a high efficiency of water dissociation for the TiO2 catalyst, a promising result for H2 generation in true aqueous environments

Insight into the X‐ray absorption spectra of Cu‐porphyrazines from electronic structure theory

Transition metal porphyrazines are a widely used class of compounds with applications in catalysis, organic solar cells, photodynamic therapy, and nonlinear optics. The most prominent members of that family of compounds are metallophtalocyanines, which have been the subject of numerous spectroscopic and theoretical studies. In this work, the electronic structure and X‐ray absorption characteristics of three Cu‐porphyrazine derivatives are investigated by means of modern electronic structure theory. More precisely, the experimentally observed N K‐edge and Cu L‐edge features are presented and reproduced by time‐dependent density functional theory, restricted open‐shell configuration interaction, and a restricted active space approach. Where possible, the calculations are used to interpret the observed spectroscopic features in terms of electronic transitions and, furthermore, to connect spectral differences to chemical variations. Part of the discussion of the computational results concerns the impact of various parameters and approximations that are used for the calculations, for example, the choice of active space

The electronic structure of the aqueous permanganate ion: aqueous-phase energetics and molecular bonding studied using liquid jet photoelectron spectroscopy

Permanganate aqueous solutions, MnO4(aq.)-, were studied using liquid-micro-jet-based soft X-ray non-resonant and resonant photoelectron spectroscopy to determine valence and core-level binding energies. To identify possible differences in the energetics between the aqueous bulk and the solution-gas interface, non-resonant spectra were recorded at two different probing depths. Similar experiments were performed with different counter ions, Na(+)and K+, with the two solutions yielding indistinguishable anion electron binding energies. Our resonant photoelectron spectroscopy measurements, performed near the Mn L-II,L-III- and O K-edges, selectively probed valence charge distributions between the Mn metal center, O ligands, and first solvation shell in the aqueous bulk. Associated resonantly-enhanced solute ionisation signals revealed hybridisation of the solute constituents' atomic orbitals, including the inner valence Mn 3p and O 2s. We identified intermolecular coulombic decay relaxation processes following resonant X-ray excitation of the solute that highlight valence MnO4(aq.)--H(2)O((l))electronic couplings. Furthermore, our results allowed us to infer oxidative reorganisation energies of MnO(4)((aq.))and adiabatic valence ionisation energies of MnO4(aq.)-, revealing the Gibbs free energy of oxidation and permitting estimation of the vertical electron affinity of MnO4(aq.). Finally, the Gibbs free energy of hydration of isolated MnO(4)(-)was determined. Our results and analysis allowed a near-complete binding-energy-scaled MnO(4)((aq.))(-)molecular orbital and a valence energy level diagram to be produced for the MnO4(aq.)-/MnO(4)((aq.))system. Cumulatively, our mapping of the aqueous-phase electronic structure of MnO(4)(-)is expected to contribute to a deeper understanding of the exceptional redox properties of this widely applied aqueous transition-metal complex ion

Auditive Wissenskulturen: Wissen, Macht und die Welt der Klänge

In der Einleitung zum Sammelband Auditive Wissenskulturen – Das Wissen klanglicher Praxis stellen die Autoren zuerst die Diskrepanzen der jeweiligen Beziehungen des Visuellen und des Auditiven zu Wissen anhand einiger Beispiele vor. Sie exemplifzieren auch, wie sowohl auditive Praxis als auch die Hervorbringung und Vermittlung von Wissen in soziale Prozesse eingebunden sind und damit einhergehend mit Machtverhältnissen in Verbindung stehen. Die Erforschung von Klang durch Sound Studies und anthropologische Studien werden genauer behandelt, ebenso Gemeinsamkeiten und Unterschiede in den Herangehensweisen an Klänge seitens der Wissenschafen und der Künste. Schließlich schlagen sie vor, den Begrif der Wissenskulturen als Forschungsstrategie zum Verstehen von auditivem Wissen zu benutzen, um explizites und implizites Wissen, wissenschafliche und künstlerische, sowie klangproduzierende Prozesse und Hörverständnis gleichermaßen innerhalb sozialer und kollektiver Felder beschreib- und analysierbar zu machen. Diese Forschungsstrategie wird anhand einer Übersicht über die Beiträge im vorliegenden Band im Detail vorgestellt

Universal singular sets in the calculus of variations

For regular one-dimensional variational problems, Ball and Nadirashvilli introduced the notion of the universal singular set of a Lagrangian $L$ and established its topological negligibility. This set is defined to be the set of all points in the plane through which the graph of some absolutely continuous $L$-minimizer passes with infinite derivative. Motivated by Tonelli's partial regularity results, the question of the size of the universal singular set in measure naturally arises. Here we show that universal singular sets are characterized by being essentially purely unrectifiable --- that is, they intersect most Lipschitz curves in sets of zero length and that any compact purely unrectifiable set is contained within the universal singular set of some smooth Lagrangian with given superlinear growth. This gives examples of universal singular sets of Hausdorff dimension two, filling the gap between previously known one-dimensional examples and Sychev's result that universal singular sets are Lebesgue null. We show that some smoothness of the Lagrangian is necessary for the topological size estimate, and investigate the relationship between growth of the Lagrangian and the existence of (pathological) rectifiable pieces in the universal singular set. We also show that Tonelli's partial regularity result is stable in that the energy of a `near' minimizer $u$ over the set where it has large derivative is controlled by how far $u$ is from being a minimizer

Spin States Protected from Intrinsic Electron-Phonon-Coupling Reaching 100 ns Lifetime at Room Temperature in MoSe2_2

We present time-resolved Kerr rotation measurements, showing spin lifetimes of over 100 ns at room temperature in monolayer MoSe$_2$. These long lifetimes are accompanied by an intriguing temperature dependence of the Kerr amplitude, which increases with temperature up to 50 K and then abruptly switches sign. Using ab initio simulations we explain the latter behavior in terms of the intrinsic electron-phonon coupling and the activation of transitions to secondary valleys. The phonon-assisted scattering of the photo-excited electron-hole pairs prepares a valley spin polarization within the first few ps after laser excitation. The sign of the total valley magnetization, and thus the Kerr amplitude, switches as a function of temperature, as conduction and valence band states exhibit different phonon-mediated inter-valley scattering rates. However, the electron-phonon scattering on the ps time scale does not provide an explanation for the long spin lifetimes. Hence, we deduce that the initial spin polarization must be transferred into spin states which are protected from the intrinsic electron-phonon coupling, and are most likely resident charge carriers which are not part of the itinerant valence or conduction band states.Comment: 18 pages, 17 figure

Multi-reference approach to the calculation of photoelectron spectra including spin-orbit coupling

X-ray photoelectron spectra provide a wealth of information on the electronic structure. The extraction of molecular details requires adequate theoretical methods, which in case of transition metal complexes has to account for effects due to the multi-configurational and spin-mixed nature of the many-electron wave function. Here, the Restricted Active Space Self-Consistent Field method including spin-orbit coupling is used to cope with this challenge and to calculate valence and core photoelectron spectra. The intensities are estimated within the frameworks of the Dyson orbital formalism and the sudden approximation. Thereby, we utilize an efficient computational algorithm that is based on a biorthonormal basis transformation. The approach is applied to the valence photoionization of the gas phase water molecule and to the core ionization spectrum of the $\text{[Fe(H}_2\text{O)}_6\text{]}^{2+}$ complex. The results show good agreement with the experimental data obtained in this work, whereas the sudden approximation demonstrates distinct deviations from experiments

Unambiguous determination of spin dephasing times in ZnO

Time-resolved magneto-optics is a well-established optical pump probe technique to generate and to probe spin coherence in semiconductors. By this method, spin dephasing times T_2^* can easily be determined if their values are comparable to the available pump-probe-delays. If T_2^* exceeds the laser repetition time, however, resonant spin amplification (RSA) can equally be used to extract T_2^*. We demonstrate that in ZnO these techniques have several tripping hazards resulting in deceptive values for T_2^* and show how to avoid them. We show that the temperature dependence of the amplitude ratio of two separate spin species can easily be misinterpreted as a strongly temperature dependent T_2^* of a single spin ensemble, while the two spin species have T_2^* values which are nearly independent of temperature. Additionally, consecutive pump pulses can significantly diminish the spin polarization, which remains from previous pump pulses. While this barely affects T_2^* values extracted from delay line scans, it results in seemingly shorter T_2^* values in RSA.Comment: 11 pages, 10 figure

CoSimPy: An open-source python library for MRI radiofrequency Coil EM/Circuit Cosimulation

Background and objectives: The Electromagnetic/Circuit cosimulation method represents a valuable and effective strategy to address those problems where a radiative structure has to interact with external supporting circuitries. This is of particular concern for Magnetic Resonance Imaging (MRI), radiofrequency (RF) coils design, where the supporting circuitry optimisation represents, generally, a crucial aspect. This article presents CoSimPy, an open-source Python circuit simulation library for Electromagnetic/Circuit cosimulations and specifically optimised for MRI, RF coils design.Methods: CoSimPy is designed following an Object-orientated programming. In addition to the essential methods aimed to performed the Electromagnetic/Circuit cosimulations, many others are implemented both to simplify the standard workflow and to evaluate the RF coils performance. In this article, the theory which underlies the fundamental methods of CoSimPy is shown together with the basic framework of the library.Results: In the paper, the reliability of CoSimPy is successfully tested against a full-wave electromagnetic simulations involving a reference setup. The library is made available httys://github.com/umbertozanovello/CoSimpy under together with a detailed documentation providing guidelines and examples. CoSimPy is distributed under the Massachusetts Institute of Technology (MIT) license.Conclusions: CoSimPy demonstrated to be an agile tool employable for Electromagnetic/Circuit cosimulations. Its distribution is meant to fulfil the needs of several researchers also avoiding duplication of effort in writing custom implementations. CoSimPy is under constant development and aims to represent a coworking environment where scientists can implement additional methods whose sharing can represent an advantage for the community. Finally, even if CoSimPy is designed with special focus on MRI, it represents an efficient and practical tool potentially employable wherever electronic devices made of radiative and circuitry components are involved. (C) 2022 Published by Elsevier B.V