| 1. |
- Abid, Abdul Rahman, et al.
(författare)
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Electron-ion coincidence spectroscopy of a large organic molecule : photofragmentation of avobenzone after valence and core ionisation
- 2020
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:24
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Tidskriftsartikel (refereegranskat)abstract
- The Avobenzone (AVOB) molecule is very photoactive and undergoes irreversible degradation upon irradiation. We studied its valence and core-level (C1s and O1s) photoionisation and subsequent photofragmentation with photoelectron spectroscopy and photoelectron-photoion-photoion coincidence (PEPIPICO) spectroscopy. AVOB is one of the largest molecules studied with this technique. The results show that the AVOB molecule dissociates into an extensive range of fragments by different pathways with little element or site-selectivity. The coincident maps were used to determine selected fragment separation sequences by analysing the slopes of patterns from ion pairs after the core ionisation. Charge delocalisation over the benzene rings and their relative stability favor fragmentation by cleavage of the bridge between them.
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| 2. |
- Abid, Abdul Rahman, et al.
(författare)
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Forming Bonds While Breaking Old Ones : Isomer-Dependent Formation of H3O+ from Aminobenzoic Acid During X-ray-Induced Fragmentation
- 2023
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 127:6, s. 1395-1401
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Tidskriftsartikel (refereegranskat)abstract
- Intramolecular hydrogen transfer, a reaction where donor and acceptor sites of a hydrogen atom are part of the same molecule, is a ubiquitous reaction in biochemistry and organic synthesis. In this work, we report hydronium ion (H3O+) production from aminobenzoic acid (ABA) after core-level ionization with soft X-ray synchrotron radiation. The formation of H3O+ during the fragmentation requires that at least two hydrogen atoms migrate to one of the oxygen atoms within the molecule. The comparison of two structural isomers, ortho- and meta-ABA, revealed that the production of H3O+ depends strongly on the structure of the molecule, the ortho-isomer being much more prone to produce H3O+. The isomer-dependency suggests that the amine group acts as a donor in the hydrogen transfer process. In the case of ortho-ABA, detailed H3O+ production pathways were investigated using photoelectron-photoion-photoion coincidence (PEPIPICO) spectroscopy. It was found that H3O+ can result from a direct two-body dissociation but also from sequential fragmentation processes.
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| 3. |
- Abid, Abdul Rahman, et al.
(författare)
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The effect of relative humidity on CaCl2 nanoparticles studied by soft X-ray absorption spectroscopy
- 2021
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 11:4, s. 2103-2111
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Tidskriftsartikel (refereegranskat)abstract
- Ca- and Cl-containing nanoparticles are common in atmosphere, originating for example from desert dust and sea water. The properties and effects on atmospheric processes of these aerosol particles depend onthe relative humidity (RH) as they are often both hygroscopic and deliquescent. We present here a study of surface structure of free-flying CaCl2 nanoparticles (CaCl2-NPs) in the 100 nm size regime prepared at different humidity levels (RH: 11–85%). We also created mixed nanoparticles by aerosolizing a solution ofCaCl2 and phenylalanine (Phe), which is a hydrophobic amino acid present in atmosphere. Information of hydration state of CaCl2-NPs and production of mixed CaCl2 + Phe nanoparticles was obtained using soft X-ray absorption spectroscopy (XAS) at Ca 2p, Cl 2p, C 1s, and O 1s edges. We also report Ca 2p andCl 2p X-ray absorption spectra of an aqueous CaCl2 solution. The O 1s X-ray absorption spectra measured from hydrated CaCl2-NPs resemble liquid-like water spectrum, which is heavily influenced by the presence of ions. Core level spectra of Ca2+ and Cl- ions do not show a clear dependence of % RH, indicating that the first coordination shell remains similar in all measured hydrated CaCl2-NPs, but they differ from aqueous solution and solid CaCl2.
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| 4. |
- Abid, Abdul Rahman
(författare)
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X-ray Absorption and Fragmentationas Initial Steps of Radiation Damage in Free Organic Molecules and Nanoparticles
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the molecular radiation damage is crucial in radiobiology, molecular physics, and atmospheric science. In this thesis, the initial steps of radiation damage of anhydrous gas-phase molecules and hydrated nanoparticles were studied using synchrotron radiation based electron-ion coincidence spectroscopy and X-ray absorption spectroscopy under vacuum conditions. Electron - ion coincidence spectroscopy was used to study the photofragmentation and molecular dynamics of the isolated gas-phase molecules. In addition to the photofragmentation of the gas-phase molecules, the effect of the initial ionization site, initial molecular geometry, and the intramolecular chemical environment has been studied. In avobenzone, core ionization leads to massive fragmentation, with a slight site-selectivity concerning fragment production. In ortho-aminobenzoic acid, core ionization leads to the production of a hydronium ion, indicating that the importance of functional group's position for double intramolecular hydrogen transfer. X-ray absorption spectroscopy was used to probe hydrated nanoparticles prepared at different relative humidities. In hydrated inorganic and mixed inorganic-organic nanoparticles, water is present in a liquid-like state. With different ranges of relative humidity, the primary hydration layers of the hydrated nanoparticles stays the same. In mixed nanoparticles, there is evidence for interaction between the included organic biomolecule with the inorganic and/or water molecules.
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| 5. |
- Ismail, Mostafa Y., et al.
(författare)
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Surface analysis of tissue paper using laser scanning confocal microscopy and micro-computed topography
- 2020
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 27:15, s. 8989-9003
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Tissue paper softness relies on two major factors, the bulk softness, which can be indicated by the elasticity of the sheet, and surface softness. Measurement of surface softness is complicated and often requires a multi-step process. A key parameter defining surface softness is the topography of the surface, particularly the crepe structure and its periodicity. Herein, we present a novel approach to measure and quantify the tissue paper surface crepe structure and periodicity based on the detection of waviness along the sample using laser scanning confocal microscopy (LSM) and X-ray tomography (XRT). In addition, field emission scanning electron microscope (FESEM) was used to characterize the tissue paper surface. We demonstrate that surface topography is directly correlated to the erosion of the doctor blade, which is used to remove the dry tissue paper from the Yankee cylinder. Because of its accuracy and simplicity, the laser confocal microscopy method has the potential to be used directly on the production line to monitor the production process of the tissue paper. XRT revealed more structural details of the tissue paper structure in 3D, and it allowed for the reconstruction of the surface and the internal structure of the tissue paper. Graphic abstract: [Figure not available: see fulltext.]
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| 6. |
- Kumagai, Yoshiaki, et al.
(författare)
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Suppression of thermal nanoplasma emission in clusters strongly ionized by hard x-rays
- 2021
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Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 54:4
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Tidskriftsartikel (refereegranskat)abstract
- Using electron and ion spectroscopy, we studied the electron and nuclear dynamics in similar to 50 000-atom large krypton clusters, following excitation with an intense hard x-ray pulse. Beyond the single pulse experiment, we also present the results of a time-resolved, x-ray pump-near-infrared probe measurement that allows one to learn about the time evolution of the system. After core ionization of the atoms by x-ray photons, trapped Auger and secondary electrons form a nanoplasma in which the krypton ions are embedded, according to the already published scenario. While the ion data show expected features, the electron emission spectra miss the expected pump-probe delay-dependent enhancement except for a slight enhancement in the energy range below 2 eV. Theoretical simulations help to reveal that, due to the deep trapping potential of the ions during the long time expansion accompanied by electron-ion recombination, thermal emission from the transient nanoplasma becomes quenched.
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| 7. |
- Patanen, Minna, et al.
(författare)
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Surface composition of size-selected sea salt particles under the influence of organic acids studied in situ using synchrotron radiation X-ray photoelectron spectroscopy
- 2022
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Ingår i: Environmental Science. - : Royal Society of Chemistry (RSC). - 2634-3606. ; 2:5, s. 1032-1040
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Tidskriftsartikel (refereegranskat)abstract
- Sea spray aerosols play a key role in the climate system by scattering solar radiation and by serving as cloud condensation nuclei. Despite their importance, the impact of sea spray aerosols on global climate remains highly uncertain. One of the key knowledge gaps in our understanding of sea spray aerosol is the chemical composition of the particle surface, important for various atmospheric chemical processes, as a function of size and bulk composition. Here, we have applied X-ray photoelectron spectroscopy (XPS) to determine the surface composition of both pure inorganic sea salt aerosols and sea salt aerosols spiked with an amino acid (phenylalanine) and a straight chain fatty acid (octanoic acid). Importantly, the use of a differential mobility analyser allowed size-selection of 150, 250 and 350 nm monodisperse aerosol particles for comparison to polydisperse aerosol particles. We observed enrichment of magnesium at the particle surfaces relative to chloride in all aerosols tested, across all particle sizes. Interestingly, the magnitude of this enrichment was dependent on the type of organic present in the solution as well as the particle size. Our results suggest that the observed enrichment in magnesium is an inorganic effect which can be either enhanced or diminished by the addition of organic substances.
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| 8. |
- Pelimanni, Eetu, et al.
(författare)
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Core and Valence Level Photoelectron Spectroscopy of Nanosolvated KCl
- 2021
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 125:22, s. 4750-4759
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Tidskriftsartikel (refereegranskat)abstract
- The solvation of alkali and halide ions in the aqueous environment has been a subject of intense experimental and theoretical research with multidisciplinary interests; yet, a comprehensive molecular-level understanding has still not been obtained. In recent years, electron spectroscopy has been increasingly applied to study the electronic and structural properties of aqueous ions with implications, especially in atmospheric chemistry. In this work, we report core and valence level (Cl 2p, Cl 3p, and K 3p) photoelectron spectra of the common alkali halide, KCl, doped in gas-phase water clusters in the size range of a few hundred water molecules. The results indicate that the electronic structure of these nanosolutions shows a distinct character from that observed at the liquid-vapor interface in liquid microjets and ambient pressure setups. Insights are provided into the unique solvation properties of ions in a nanoaqueous environment, emerging properties of bulk electrolyte solutions with growing cluster size, and sensitivity of the electronic structure to varying solvation configurations.
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| 9. |
- Pelimanni, Eetu, et al.
(författare)
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Solvent and cosolute dependence of Mg surface enrichment in submicron aerosol particles
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:5, s. 2934-2943
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Tidskriftsartikel (refereegranskat)abstract
- The formation of multicomponent aerosol particles from precursor solution droplets often involves segregation and surface enrichment of the different solutes, resulting in non-homogeneous particle structures and diverse morphologies. In particular, these effects can have a significant influence on the chemical composition of the particle-vapor interface. In this work, we investigate the bulk/surface partitioning of inorganic ions, Na+, Mg2 +, Ca2 +, Cl- and Br-, in atomiser-generated submicron aerosols using synchrotron radiation based X-ray photoelectron spectroscopy (XPS). Specifically, the chemical compositions of the outermost few nm thick surface layers of non-supported MgCl2/CaCl2 and NaBr/MgBr2 particles are determined. It is found that in MgCl2/CaCl2 particles, the relative abundance of the two species in the particle surface correlates well with their mixing ratio in the parent aqueous solution. In stark contrast, extreme surface enrichment of Mg2 + is observed in NaBr/MgBr2 particles formed from both aqueous and organic solution droplets, indicative of core-shell structures. Structural properties and hydration state of the particles are discussed.
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| 10. |
- Rani, Ekta, et al.
(författare)
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Unraveling compensation between electron transfer and strain in Ni-Ag-MoS 2 photocatalyst
- 2022
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 414, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- Despite the boom in catalytic response via constructing interfaces, understanding interfaces’ interaction in heterostructures is still a paradox. In this work, the interaction of Ni with MoS2 in Ni-Ag-MoS2 heterostructure are unveiled through synchrotron X-PEEM and what's more, the missing interaction mechanism at the Ag-MoS2 interface is probed via Raman mapping. The observed competition between the downshift of the E2g1 and A1g modes due to charge carrier injection and the upshift of the E2g1 and A1g modes due to compressive strain during reverse laser power experiment is assigned to the non-uniform growth of Ag nanoparticles, their intimate contact with MoS2, and Ag intercalated layered MoS2. The substantial improvement of the H2 yield of the Ni-Ag-MoS2 (∼55 μmol h−1 g−1) over the pristine MoS2 and the binary Ag-MoS2 evidence successful bonding of Ni, Ag and MoS2. This study highlights the importance of considering both electronic coupling and strain to optically tune electromechanical properties of MoS2.
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