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Abstract: We describe a joint experimental and theoretical investigation on oxygen double photoionization—the emission of two electrons from atomic oxygen following single photon absorption. High-resolution experimental measurements were performed at the Advanced Light Source, revealing sharp resonance structure superimposed on the more familiar Wannier-like, nearly-linear background. These resonance features are attributed to ionization-plus-excitation Feshbach resonances embedded in the double ionization continuum, doubly-excited states that lie above the double-ionization threshold. Such features are absent in the double photoionization cross section of He, or other quasi-two-electron systems, for which the doubly-ionized atomic core remains inert. For a corresponding theoretical analysis, the R-matrix with pseudostates (RMPS) method was invoked by calculating final-state, two-electron resonances-plus-continua wavefunctions and corresponding single-photon absorption cross sections. Overall agreement is found in the direct, background double photoionization cross section. However, the RMPS method, using a small basis due to practical computational limitations, was unable to reproduce quantitatively the smooth background or the sharper resonance features observed in the measurements, showing instead large-scale oscillations about the experimental background, and characteristic pseudoresonance jitter, associated with an insufficient convergence of the pseudostate representation to the true two-electron infinite series of Feshbach resonances embedded in the two-electron continuum. The prominent resonance structure observed highlights the need to consider multiple excitation processes in atoms more complex than He or quasi-two-electron systems.

The new Microscopic and Electronic Structure Observatory (MAESTRO) at the Advanced Light Source (ALS) in Berkeley provides X-rays of variable polarization, produced by an elliptically polarized undulator (EPU), for angle resolved photoemission (ARPES) and photoemission electron microscopy (PEEM) experiments. The interpretation of photoemission data, in particular of dichroism effects in ARPES, requires the precise knowledge of the exact polarization state. Numerical simulations show that the first harmonics of the EPU at MAESTRO provides soft X-rays of almost 100% on axis polarization. However, the higher harmonics as well as the downstream optical elements of the beamline, have a considerable impact on the polarization of the light delivered to the experimental end-station. Employing a simple reflective polarimeter, the polarization is characterized for variable EPU and beamline settings and the overall degree of polarization in the MAESTRO end-stations is estimated to be on the order of 83%.

The sources and nature of organic carbon on Mars have been a subject of intense research. Steele et al. (2012) showed that 10 martian meteorites contain macromolecular carbon phases contained within pyroxene- and olivine-hosted melt inclusions. Here, we show that martian meteorites Tissint, Nakhla, and NWA 1950 have an inventory of organic carbon species associated with fluid-mineral reactions that are remarkably consistent with those detected by the Mars Science Laboratory (MSL) mission. We advance the hypothesis that interactions among spinel-group minerals, sulfides, and a brine enable the electrochemical reduction of aqueous CO2 to organic molecules. Although documented here in martian samples, a similar process likely occurs wherever igneous rocks containing spinel-group minerals and/or sulfides encounter brines.

Absolute absorption and photoionization cross sections of methane have been measured with an accuracy of about 2% or 3% over most of the wavelength range from 950 to 110 Å. Also, dissociative photoionization cross sections were measured for the production of CH+4 , CH+3 , CH+2 , CH+, and C+ from their respective thresholds to 159 Å, and for H+ and H+2 measurements were made down to 240 Å. Fragmentation was observed at all excited ionic states of CH4. [ABSTRACT FROM AUTHOR]

Stromatolites composed of apatite occur in post-Lomagundi-Jatuli successions (late Palaeoproterozoic) and suggest the emergence of novel types of biomineralization at that time. The microscopic and nanoscopic petrology of organic matter in stromatolitic phosphorites might provide insights into the suite of diagenetic processes that formed these types of stromatolites. Correlated geochemical micro-analyses of the organic matter could also yield molecular, elemental and isotopic compositions and thus insights into the role of specific micro-organisms among these communities. Here, we report on the occurrence of nanoscopic disseminated organic matter in the Palaeoproterozoic stromatolitic phosphorite from the Aravalli Supergroup of north-west India. Organic petrography by micro-Raman and Transmission Electron Microscopy demonstrates syngeneity of the organic matter. Total organic carbon contents of these stromatolitic phosphorite columns are between 0.05 and 3.0 wt% and have a large range of δ13Corg values with an average of -18.5‰ (1σ = 4.5‰). δ15N values of decarbonated rock powders are between -1.2 and +2.7‰. These isotopic compositions point to the important role of biological N2-fixation and CO2-fixation by the pentose phosphate pathway consistent with a population of cyanobacteria. Microscopic spheroidal grains of apatite (MSGA) occur in association with calcite microspar in microbial mats from stromatolite columns and with chert in the core of diagenetic apatite rosettes. Organic matter extracted from the stromatolitic phosphorites contains a range of molecular functional group (e.g. carboxylic acid, alcohol, and aliphatic hydrocarbons) as well as nitrile and nitro groups as determined from C- and N-XANES spectra. The presence of organic nitrogen was independently confirmed by a CN- peak detected by ToF-SIMS. Nanoscale petrography and geochemistry allow for a refinement of the formation model for the accretion and phototrophic growth of stromatolites. The original microbial biomass is inferred to have been dominated by cyanobacteria, which might be an important contributor of organic matter in shallow-marine phosphorites. [ABSTRACT FROM AUTHOR]

Introduction: Macromolecular organic matter in primitive small body materials is one of the reliable indicators to determine the chemical evolution in the early Solar System. JAXA's Hayabusa2 mission explored the carbonaceous asteroid Ryugu and collected its surface materials [1]. On December 6, 2020, the asteroid sample was returned to the Earth. Through the curatorial work at JAXA, it was reported that the Ryugu samples contain high abundances of hydrous minerals and organic matter [2, 3]. Afterward, the initial sample analysis has started from June 2021 to classify and characterize the Ryugu samples in the context of the Solar System formation. In order to uncover the significance of organic matter on C-type asteroid, the Initial Analysis Organic Macromolecule team unveiled the chemical, isotopic, and morphological compositions of macromolecular organic matter from the Ryugu samples. Samples and Methods: Chamber A aggregates (A0108) and Chamber C aggregates (C0109) collected at the first and second touchdown sites, respectively, have been analyzed. The individual intact grains from A0108 and C0109 range from 200 to 900 µm in size. Additional aggregates from Chamber A (A0106) and Chamber C (C0107) were transferred from the Soluble Organic Molecules team after their water and solvent extractions, and were treated with 6M HCl and 1M HCl/9M HF to yield insoluble organic matter (IOM) at Hiroshima University [4]. The main stream of the analytical procedures included a combination of µ-FTIR, µ-Raman spectroscopy, synchrotron-based STXMXANES, STEM-EELS-EDS, AFM-IR, NanoSIMS [4]. Additional protocols by Xe-PFIB, TXM, XRF, Solid-state 1H and 13C NMR, ToF-SIMS, Visible spectroscopy, and AFM have been included for the latter half of the initial analysis. EA-IRMS and noble gas isotope analysis of Ryugu IOM were also performed in collaboration with Soluble organic molecule (SOM) team [5] and Volatile team [6], respectively. Results and discussion: Macromolecular organic matter were abundant and has complex structures consisting of aromatic carbons, aliphatic carbons, ketones and carboxyls [7, 8]. The functional group compositions are typically seen in IOM from CI and CM chondrites. The functional group variations correlated with the morphologies of nanosized organic matter; organic nanoglobules and nanoparticles are aromatic-rich, while organic matter mixed with Mgrich phyllosilicate matrix and carbonates are IOM-like or diffuse carbon [8, 9]. The observed functional group diversity is likely influenced by aqueous evolution on the asteroid parent body without significant heating event. The dD distributions of Ryugu IOM from the Ryugu samples were within the dD range of CM, CI, and Tagish Lake chondrites [10]. The d15N of bulk C and insoluble organics from the Ryugu samples showed similar values to those from CI chondrites [10]. Extreme D and/or 15N enrichments or depletions in some carbonaceous grains could possibly have been derived from the solar nebula or protosolar molecular cloud. A very small fraction of carbonaceous particles show anomalous carbon isotopes including presolar SiC grains [11]. Ryugu organic matter likely resulted from heterogeneous aqueous processing that occurred on carbonaceous asteroids from the common primordial materials formed at an earlier stage of the solar nebula. These results proved the direct link between macromolecular organic matter in the carbonaceous asteroid and that in primitive carbonaceous chondrites. [ABSTRACT FROM AUTHOR]

OBJECTIVE--To assess the use of acute coronary care facilities in the Republic of Ireland with regard to case mix, patient characteristics, mortality and factors associated with mortality, time intervals to admission, utilisation of thrombolysis, and risk factor profiles. DESIGN--A 1 week prospective census of all hospitals admitting acute coronary cases. These comprised 23 coronary care units (CCU) and 17 combined coronary care/intensive care units (CCU/ICU). Data were collected by standardised methods on each new patient "upon whom a cardiac monitor was placed". RESULTS--Acute coronary heart disease was confirmed in 185 (44.9%) of 412 patients. Of these 109 (26.4%) had a confirmed myocardial infarction and 76 (18.4%) unstable angina. Women were significantly older than men in all groups. Of those with proven acute coronary heart disease, 42.6% were current smokers, 23.1% were aware of having a raised cholesterol concentration, and 42.3% gave a history of prior hypertension. Only 44% were transported by ambulance. Median delay time from the onset of symptoms to admission was 6 h in Dublin and 4 h elsewhere. 34.9% of patients with a confirmed myocardial infarction received thrombolysis. Mortality of patients with myocardial infarction CCU/ICU at 7 days was 10.9 %. CONCLUSIONS--There is potential for considerable improvement in the management of coronary heart disease in the Republic of Ireland through a reduction in delay times to admission to hospital, increased use of thrombolytic treatment, and intensification of advice on primary and secondary risk factors. [ABSTRACT FROM PUBLISHER]

Samples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by the Hayabusa2 spacecraft. We investigated the macromolecular organic matter in Ryugu samples and found that it contains aromatic and aliphatic carbon, ketone, and carboxyl functional groups. The spectroscopic features of the organic matter are consistent with those in chemically primitive carbonaceous chondrite meteorites that experienced parent-body aqueous alteration (reactions with liquid water). The morphology of the organic carbon includes nanoglobules and diffuse carbon associated with phyllosilicate and carbonate minerals. Deuterium and/or nitrogen-15 enrichments indicate that the organic matter formed in a cold molecular cloud or the presolar nebula. The diversity of the organic matter indicates variable levels of aqueous alteration on Ryugu's parent body.

We report on the design and performance of a double-sided coincidence velocity map imaging spectrometer optimized for electron-ion and ion-ion coincidence experiments studying inner-shell photoionization of gas-phase molecules with soft X-ray synchrotron radiation. The apparatus employs two microchannel plate detectors equipped with delay-line anodes for coincident, time- and position-resolved detection of photoelectrons and Auger electrons with kinetic energies up to 300 eV on one side of the spectrometer and photoions up to 25 eV per unit charge on the opposite side. We demonstrate its capabilities by measuring valence photoelectrons and ion spectra of neon and nitrogen and by studying channel-resolved photoelectron and Auger spectra along with fragment-ion momentum correlations for chlorine 2p inner-shell ionization of cis- and trans-1,2-dichloroethene.

Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising high energy densities for lithium-ion batteries. However, anion redox is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li 1.17-x Ni 0.21 Co 0.08 Mn 0.54 O 2 , these properties arise from a strong coupling between anion redox and cation migration. We combine various X-ray spectroscopic, microscopic, and structural probes to show that partially reversible transition metal migration decreases the potential of the bulk oxygen redox couple by > 1 V, leading to a reordering in the anionic and cationic redox potentials during cycling. First principles calculations show that this is due to the drastic change in the local oxygen coordination environments associated with the transition metal migration. We propose that this mechanism is involved in stabilizing the oxygen redox couple, which we observe spectroscopically to persist for 500 charge/discharge cycles.

The fragmentation dynamics of 2,6- and 3,5-difluoroiodobenzene after iodine 4d inner-shell photoionization with soft X-rays are studied using coincident electron and ion momentum imaging. By analyzing the momentum correlation between iodine and fluorine cations in three-fold ion coincidence events, we can distinguish the two isomers experimentally. Classical Coulomb explosion simulations are in overall agreement with the experimentally determined fragment ion kinetic energies and momentum correlations and point toward different fragmentation mechanisms and time scales. While most three-body fragmentation channels show clear evidence for sequential fragmentation on a time scale larger than the rotational period of the fragments, the breakup into iodine and fluorine cations and a third charged co-fragment appears to occur within several hundred femtoseconds.

Fluid phase transitions inside single, isolated carbon nanotubes are predicted to deviate substantially from classical thermodynamics. This behaviour enables the study of ice nanotubes and the exploration of their potential applications. Here we report measurements of the phase boundaries of water confined within six isolated carbon nanotubes of different diameters (1.05, 1.06, 1.15, 1.24, 1.44 and 1.52 nm) using Raman spectroscopy. The results reveal an exquisite sensitivity to diameter and substantially larger temperature elevations of the freezing transition (by as much as 100 °C) than have been theoretically predicted. Dynamic water filling and reversible freezing transitions were marked by 2-5 cm -1 shifts in the radial breathing mode frequency, revealing reversible melting bracketed to 105-151 °C and 87-117 °C for 1.05 and 1.06 nm single-walled carbon nanotubes, respectively. Near-ambient phase changes were observed for 1.44 and 1.52 nm nanotubes, bracketed between 15-49 °C and 3-30 °C, respectively, whereas the depression of the freezing point was observed for the 1.15 nm nanotube between -35 and 10 °C. We also find that the interior aqueous phase reversibly decreases the axial thermal conductivity of the nanotube by as much as 500%, allowing digital control of the heat flux.

This study assesses the quantitative effects of incorporating high-volume fly ash (HVFA) into tricalcium silicate (C₃S) paste on the hydration, degree of silicate polymerization, and Al substitution for Si in calcium silicate hydrate (C-S-H). Thermogravimetric analysis and isothermal conduction calorimetry showed that, although the induction period of C₃S hydration was significantly extended, the degree of hydration of C₃S after the deceleration period increased due to HVFA incorporation. Synchrotron-sourced soft X-ray spectromicroscopy further showed that most of the C₃S in the C₃S-HVFA paste was fully hydrated after 28 days of hydration, while that in the pure C₃S paste was not. The chemical shifts of the Si K edge peaks in the near-edge X-ray fine structure of C-S-H in the C₃S-HVFA paste directly indicate that Al substitutes for Si in C-S-H and that the additional silicate provided by the HVFA induces an enhanced degree of silicate polymerization. This new spectromicroscopic approach, supplemented with 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy and transmission electron microscopy, turned out to be a powerful characterization tool for studying a local atomic binding structure of C-S-H in C₃S-HVFA system and presented results consistent with previous literature.

An experimental route to identify and separate geometric isomers by means of coincident Coulomb explosion imaging is presented, allowing isomer-resolved photoionization studies on isomerically mixed samples. We demonstrate the technique on cis/trans 1,2-dibromoethene (C 2 H 2 Br 2 ). The momentum correlation between the bromine ions in a three-body fragmentation process induced by bromine 3d inner-shell photoionization is used to identify the cis and trans structures of the isomers. The experimentally determined momentum correlations and the isomer-resolved fragment-ion kinetic energies are matched closely by a classical Coulomb explosion model.

The understanding and control of early hydration of tricalcium silicate (C₃S) is of great importance to cement science and concrete technology. However, traditional characterization methods are incapable of providing morphological and spectroscopic information about in situ hydration at the nanoscale. Using soft X-ray spectromicroscopy, we report the changes in morphology and molecular structure of C₃S at an early stage of hydration. In situ C₃S hydration in a wet cell, beginning with induction (~1 h) and acceleration (~4 h) periods of up to ~8 h, was studied and compared with ex situ measurements in the deceleration period after 15 h of curing. Analysis of the near-edge X-ray absorption fine structure showed that the Ca binding energy and energy splitting of C₃S changed rapidly in the early age of hydration and exhibited values similar to calcium silicate hydrate (C-S-H). The formation of C-S-H nanoseeds in the C₃S solution and the development of a fibrillar C-S-H morphology on the C₃S surface were visualized. Following this, silicate polymerization accompanied by C-S-H precipitation produced chemical shifts in the peaks of the main Si K edge and in multiple scattering. However, the silicate polymerization process did not significantly affect the Ca binding energy of C-S-H.

The high brightness of the bend magnets at the Advanced Light Source has been exploited to illuminate a scanning transmission X-ray microscope (STXM). This is the first diffraction-limited scanning X-ray microscope to operate with a useful count rate on a synchrotron bend-magnet source. A simple dedicated beamline has been built covering the range of photon energy from 250 eV to 600 eV. The beamline is always available and needs little adjustment. Use of this facility is much easier than that of installations that share undulator beams. This facility provides radiation for C 1s, N 1s and O 1s near-edge X-ray absorption spectromicroscopy with STXM count rates in excess of 1 MHz and with spectral resolution typically 1:2000, limited to about 1:5000.