33 research outputs found
Vibration dependent branching and photoelectron angular distributions observed across the Cooper minimum region of bromobenzene
Vibrational state-resolved photoelectron anisotropy parameters, beta, for the ~X 2B1, ~B 2B2, and ~C2B1 state ionizations of bromobenzene have been recorded at photon energies ranging from 20.5 to 94 eV, so spanning the region of the expected bromine Cooper minimum (CM). The ~X state displays no CM and its beta value is also independent of vibrational level, in accord with the Franck-Condon Approximation. The ~B and ~ C state beta values display the CM to differing degrees, but both show a vibrational dependence that extends well below the obvious CM dip. Calculations are presented that replicate these observations of Franck-Condon Approximation breakdown spanning an extended photon energy range. This is the first demonstration of such wide-ranging breakdown detected in the beta anisotropy parameter in the absence of any resonance. Measured and calculated vibrational branching ratios for these states are also presented. Although the ~B state branching ratios remain constant, in accord with Franck-Condon expectations, the ~X and (especially) the ~C state ratios display weak, quasi-linear variations across the studied range of photon energy, but with no apparent correlation with the CM position
Efficient neutralization of core ionized species in an aqueous environment
Abstract
Core ionization dynamics of argonâwater heteroclusters ArM[HâO]N are investigated using a site and process selective experimental scheme combining 3 keV electron irradiation with Auger electronâionâion multi-coincidence detection. The formation of Ar 2pâťÂš vacancies followed by non-radiative decay to intermediate one-site doubly ionized states Ar²âş(3pâťÂ˛)âArMâ1[HâO]N and subsequent redistribution of charge to the cluster environment are monitored. At low argon concentrations the emission of an [HâO]nâ˛Hâş/[HâO]nâ˛â˛Hâş ion pair is the dominant outcome, implying on high efficiency of charge transfer to the water network. Increasing the condensation fraction of argon in the mixed clusters and/or to pure argon clusters is reflected as a growing yield of Armâ˛+/Armâ˛â˛+ ion pairs, providing a fingerprint of the precursor heterocluster beam composition. The coincident Auger electron spectra, resolved with better than 1 eV resolution, show only subtle differences and thereby reflect the local nature of the initial Auger decay step. The results lead to better understanding of inner shell ionization processes in heterogeneous clusters and in aqueous environments in general
15th international conference on electronic spectroscopy and structure:book of abstracts
Welcome to ICESS 15th
Welcome to the 15th ICESS conference! Finally, after five years of waiting it is our pleasure to
welcome you - the whole international community â to Oulu, Finland. The scientific program built in
collaboration with international advisory board (IAB) covers widely the areas of research and surely
engages plenty of discussions and ideas for future collaborations. Great thanks for participating and
making the event possible! Let us all make the event pleasant respecting the diversity and
committing to strengthening the international community of ICESS.
Welcome to Oulu!
ICESS local committee:
Marko Huttula, chair
Minna Patanen, program committee
Samuli Urpelainen, Satu Ojala, local organizatio
Disentangling Auger decays in Oâ by photoelectron-ion coincidences
Abstract
In non-resonant Auger electron spectroscopies, multi core-ionized states lead to numerous energetically close-lying electronic transitions in Auger spectra, this hampering the assignment and interpretation of the experimental results. Here we reveal a new method to overcome this intrinsic limitation of non-resonant inner-shell spectroscopies. In a proof-of-principle experiment performed for the Oâ molecule, most of the Auger final states are dissociative, and we measure in coincidence the kinetic energy of the photoelectron and the kinetic energy release of the (Oâş, Oâş) ion pairs produced after the Auger decay of the O 1sâ1 core-ionized states. The Auger final states are assigned using energy conservation. We fully separate the contributions from the â´ÎŁâ and ²Σâ intermediate ionic states and conclusively demonstrate that the Auger decay probability can dramatically depend on the different Oâ 1sâ1 intermediate multiplet states. In addition, a metastable Auger final state also exists, with lifetime longer than 3.8âÎźs, and clear changes are observed in both branching ratio and spectral profile of the O 1s photoelectron spectrum when they are recorded in coincidence with either Oââşâş or with other ionic species. These changes are attributed to the population of the metastable Bâ˛ÂłÎŁâu(νâ˛â˛=0) Auger final state via different intermediate states
Influence of organic acids on the surface composition of sea spray aerosol
Abstract
Recent studies on sea spray aerosol indicate an enrichment of Ca2+ in small particles, which are often thought to originate from the very surface of a water body when bubbles burst. One model to explain this observation is the formation of ion pairs between Ca2+(aq) and surface-active organic species. In this study, we have used X-ray photoelectron spectroscopy to probe aqueous salt solutions and artificial sea spray aerosol to study whether ion pairing in the liquid environment also affects the surface composition of dry aerosol. Carboxylic acids were added to the sample solutions to mimic some of the organic compounds present in natural seawater. Our results show that the formation of a coreâshell structure governs the surface composition of the aerosol. The coreâshell structure contrasts previous observations of the dry sea spray aerosol on substrates. As such, this may indicate that substrates can impact the morphology of the dried aerosol
Solvent and cosolute dependence of Mg surface enrichment in submicron aerosol particles
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 particleâvapor interface. In this work, we investigate the bulk/surface partitioning of inorganic ions, Naâş, Mg² âş, Ca² âş, Clâť and Brâť, 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 MgClâ/CaClâ and NaBr/MgBrâ particles are determined. It is found that in MgClâ/CaClâ 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 âş is observed in NaBr/MgBrâ particles formed from both aqueous and organic solution droplets, indicative of coreâshell structures. Structural properties and hydration state of the particles are discussed
Vibration-dependent photoelectron angular distributions and branching ratios observed across the Cooper-minimum region of bromobenzene
Abstract
Vibrational state-resolved photoelectron anisotropy parameters, β, for the ËX2B1, ËB2B2, and ËC2B1 state ionizations of bromobenzene have been recorded at photon energies ranging from 20.5 to 94 eV, thus spanning the region of the expected bromine Cooper minimum (CM). The ËX state displays no CM and its β value is also independent of vibrational level, in accord with the Franck-Condon approximation. The ËB and ËC state β values display the CM to differing degrees, but both show a vibrational dependence that extends to energies well below the obvious CM dip. Calculations are presented that replicate these observations. We thus demonstrate a wide-ranging Franck-Condon approximation breakdown detected in the β anisotropy parameter in the absence of any resonance. Measured and calculated vibrational branching ratios for these states are also presented. Although the ËB state branching ratios remain constant, in accord with Franck-Condon expectations, the ËX and (especially) the ËC state ratios display weak, quasilinear variations across the studied range of photon energy, but with no apparent correlation with the CM position
Electronâion coincidence spectroscopy of a large organic molecule:photofragmentation of avobenzone after valence and core ionisation
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 photoelectronâphotoionâphotoion 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
Surface analysis of tissue paper using laser scanning confocal microscopy and micro-computed topography
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
Hybrid films of cellulose nanofibrils, chitosan and nanosilica:structural, thermal, optical, and mechanical properties
Abstract
Organic-inorganic hybrid films were fabricated from cellulose nanofibrils (CNF) and nanosilica (5â30% wt) embedded in a chitosan (Chi) biopolymer matrix using a slow evaporation method. The self-standing films exhibited high strength and modulus up to 120âÂąâ5âMPa and 7.5âÂąâ0.4âGPa, respectively, which are remarkably high values for biopolymer/chitosan hybrids. Scanning electron microscopy showed that the nanosilica is formed of larger aggregates within the lamellar CNF network structure. This observation was further confirmed using synchrotron-based scanning transmission x-ray microscopy (STXM) with the capability to determine the spatial and chemical distribution analysis of the constituents of films. It is interesting that the thermal stability of the hybrid films improved as the nanosilica content increased. Furthermore, the nanosilica effectively filled the pores in the CNF network, thus decreasing the UV transmission and the visible light transmittance of the films