Structures of small mixed krypton-xenon clusters

Structures of small mixed krypton-xenon clusters of different compositions with an average size of 30–37 atoms are investigated. The Kr 3d 5/2 and Xe 4d 5/2surface core level shifts and photoelectron intensities originating from corner, edge, and face/bulk sites are analyzed by using soft x-ray photoelectron spectroscopy. Structural models are derived from these experiments, which are confirmed by theoretical simulation taking induced dipole interactions into account. It is found that one or two small Xe cores are partly embedded in the surface of the Kr clusters. These may grow and merge leading to a phase separation between the two rare gas moieties in mixed clusters with increasing the Xe content

Structures of mixed argon-nitrogen clusters

The structures of mixed argon-nitrogen clusters of different compositions are investigated by analyzing core level shifts and relative intensities of surface and bulk sites in the Ar 2p 3/2 regime in soft X-ray photoelectron spectroscopy. These structures are confirmed by core level shift calculations taking induced dipole interactions into account, in which several model structures of the mixed clusters are considered by Monte Carlo simulations. These results suggest that the mixed argon-nitrogen clusters show partial core-shell structures, where an argon core is partially covered by nitrogen molecules

Uncovering the Charge Transfer between Carbon Dots and Water by In Situ Soft X-ray Absorption Spectroscopy.

Carbon dots (CDs) exhibit outstanding physicochemical properties that render them excellent materials for various applications, often occurring in an aqueous environment, such as light harvesting and fluorescence bioimaging. Here we characterize the electronic structures of CDs and water molecules in aqueous dispersions using in situ X-ray absorption spectroscopy. Three types of CDs with different core structures (amorphous vs graphitic) and compositions (undoped vs nitrogen-doped) were investigated. Depending on the CD core structure, different ionic currents generated upon X-ray irradiation of the CD dispersions at the carbon K-edge were detected, which are interpreted in terms of different charge transfer to the surrounding solvent molecules. The hydrogen bonding networks of water molecules upon interaction with the different CDs were also probed at the oxygen K-edge. Both core graphitization and nitrogen doping were found to endow the CDs with enhanced electron transfer and hydrogen bonding capabilities with the surrounding water molecules.Volkswagen foundation (Freigeist Fellowship No. 89592), Christian Doppler Research Association (Austrian Federal Ministry for Digital and Economic Affairs National Foundation for Research, Technology and Development) OMV

<i>In Situ</i> Soft X‑ray Absorption Spectroscopy Applied to Solid–Liquid Heterogeneous Cyanopyrazine Hydration Reaction on Titanium Oxide Catalyst

In conventional <i>in situ</i> spectroscopies of solid–liquid heterogeneous catalytic reactions, it is difficult to measure the conversion of liquid substrates on solid catalysts due to the lack of sensitivity and the difficulty in separation of target signals in the mixture of substrates, reactants, products, solvents, and solid catalysts. Element-specific soft X-ray absorption spectroscopy (XAS) is a promising method to detect target substrate and product separately from the other components using chemically different inner shell excitation energies. In the present work, we have developed an <i>in situ</i> sample cell to measure time- and temperature-dependent XAS spectra in transmission mode and applied it to one of the solid–liquid heterogeneous catalytic reactions, cyanopyrazine (PzCN) hydration to produce pyrazinamide (PzCONH₂) on the TiO₂ catalyst (PzCN + H₂O → PzCONH₂). We have succeeded in unambiguous observation of the spectral change in the C K-edge and N K-edge XAS due to the production of PzCONH₂ from PzCN during the reaction regardless of the coexistence of the bulk liquid components, H₂O (reactant) and EtOH (solvent). Furthermore, we have obtained reasonable kinetic properties in the PzCN hydration reaction from the spectral analysis such as the reaction order (first order), the rate constant, and the activation energy. Thus, the present method can be widely applicable to distinguish the minor liquid components in chemical reactions

Demonstration of Transmission Mode Soft X-ray NEXAFS Using Third- and Fifth-Order Harmonics of FEL Radiation at SACLA BL1

We demonstrate the applicability of third- and fifth-order harmonics of free-electron laser (FEL) radiation for soft X-ray absorption spectroscopy in the transmission mode at SACLA BL1, which covers a photon energy range of 20 to 150 eV in the fundamental FEL radiation. By using the third- and fifth-order harmonics of the FEL radiation, we successfully recorded near-edge X-ray absorption fine structure (NEXAFS) spectra for Ar 2p core ionization and CO2 C 1s and O 1s core ionizations. Our results show that the utilization of third- and fifth-order harmonics can significantly extend the available photon energies for NEXAFS spectroscopy using an FEL and opens the door to femtosecond pump-probe NEXAFS using a soft X-ray FEL

Aqueous-phase behavior of glyoxal and methylglyoxal observed with carbon and oxygen K-edge X-ray absorption spectroscopy

Glyoxal (CHOCHO) and methylglyoxal (CH3C(O)CHO) are well-known components of atmospheric particles and their properties can impact atmospheric chemistry and cloud formation. To get information on their hydration states in aqueous solutions and how they are affected by the addition of inorganic salts (sodium chloride (NaCl) and sodium sulfate (Na2SO4)), we applied carbon and oxygen K-edge X-ray absorption spectroscopy (XAS) in transmission mode. The recorded C K-edge spectra show that glyoxal is completely hydrated in the dilute aqueous solutions, in line with previous studies. For methylglyoxal, supported by quantum chemical calculations we identified not only C-H, C=O and C-OH bonds, but also fingerprints of C-OH(CH2) and C=C bonds. The relatively low intensity of C=O transitions implies that the monohydrated form of methylglyoxal is not favored in the solutions. Instead, the spectral intensity is stronger in regions where products of aldol condensation and enol tautomers of the monohydrates contribute. The addition of salts was found to introduce only very minor changes to absorption energies and relative intensities of the observed absorption features, indicating that XAS in the near-edge region is not very sensitive to these intermolecular organic-inorganic interactions at the studied concentrations. The identified structures of glyoxal and methylglyoxal in an aqueous environment support the uptake of these compounds to the aerosol phase in the presence of water and their contribution to secondary organic aerosol formation.Peer reviewe