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Tidal disruption events (TDEs) are rare transients, which are considered as promising tools for probing supermassive black holes in quiescent galaxies. The majority of the ≈60 known TDEs have been discovered with time-domain surveys in the last two decades. Currently, ≈10 TDEs are discovered per year, and this number will increase with the Legacy Survey of Space and Time (LSST) at the Rubin Observatory. This work evaluates LSST survey strategies in view of their performance in identifying TDEs. We assume that TDEs can be identified photometrically based on their colors, particularly in the u band, and will be scientifically useful if we can detect the light-curve peak to derive physical quantities. We define the requirements for the Rubin light curves that are needed to achieve this (detections prepeak, postpeak, and in different bands to measure color). We then inject model light curves into the Operations Simulator and calculate the fractions of TDEs passing our requirements for several strategies. We find that under the baseline strategy, ≈1.5% of simulated TDEs fulfill our detection criteria, while this number increases when more time is devoted to u -band observations. An ideal observing strategy for the photometric identification of TDEs would have longer u -band exposures, which should not come at the expense of fewer u -band visits. A filter distribution weighted toward more observing time in bluer bands, intranight visits in different filters, and strategies with frequent sampling leading to higher-quality light curves are preferred. We find that these strategies benefiting TDE science do not impact significantly other science cases.

We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the carbon disulphide CS_{2} molecule near the sulfur K-absorption edge. We observe a strong evolution of the RIXS spectral profile with the excitation energy tuned below the lowest unoccupied molecular orbital (LUMO) absorption resonance. The reason for this is twofold. Reducing the photon energy in the vicinity of the LUMO absorption resonance leads to a relative suppression of the LUMO contribution with respect to the emission signal from the higher unoccupied molecular orbitals, which results in the modulation of the total RIXS profile. At even larger negative photon-energy detuning from the resonance, the excitation-energy dependence of the RIXS profile is dominated by the onset of electron dynamics triggered by a coherent excitation of multiple electronic states. Furthermore, our study demonstrates that in the hard x-ray regime, localization of the S 1s core hole occurs in CS_{2} during the RIXS process because of the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Core-hole localization leads to violation of the symmetry selection rules for the electron transitions observed in the spectra.

The presence of doubly excited states (DESs) above the core-hole ionization threshold nontrivially modulates the x-ray absorption because the participator Auger decay couples DESs to the underlying low-energy core-hole continuum. We show that coupling also affects the high-energy continuum populated by the spectator Auger decay of DESs. For the K-L_{23}^{2} Auger decay of the 1s^{-1}3p^{-1}4s^{2}^{1}P state in argon, the competing nonresonant path is assigned to the recapture of the 1s photoelectron caused by emission of the fast electron from the shake-up K-L_{23}^{2} decay of the 1s^{-1} ion.

Single-photon multiple photoionization results from electron correlations that make this process possible beyond the independent electron approximation. To study this phenomenon experimentally, the detection in coincidence of all emitted electrons is the most direct approach. It provides the relative contribution of all possible multiple ionization processes, the energy distribution between electrons that can reveal simultaneous or sequential mechanisms, and, if possible, the angular correlations between electrons. In the present work, we present a new magnet design of our magnetic bottle electron spectrometer that allows the detection of multiply charged Xe n + ions in coincidence with n electrons. This new coincidence detection allows more efficient extraction of minor channels that are otherwise masked by random coincidences. The proof of principle is provided for xenon triple ionization.

X-ray Raman spectroscopy (XRS) is an emerging spectroscopic technique that utilizes inelastic scattering of hard X-rays to study X-ray absorption edges of low Z elements in bulk material. It was used to identify and quantify the amount of carbonyl bonds in a cathode sample, in order to track the redox reaction inside metal-organic batteries during the charge/discharge cycle. XRS was used to record the oxygen K-edge absorption spectra of organic polymer cathodes from different multivalent metal-organic batteries. The amount of carbonyl bond in each sample was determined by modeling the oxygen K-edge XRS spectra with the linear combination of two reference compounds that mimicked the fully charged and the fully discharged phases of the battery. To interpret experimental XRS spectra, theoretical calculations of oxygen K-edge absorption spectra based on density functional theory were performed. Overall, a good agreement between the amount of carbonyl bond present during different stages of battery cycle, calculated from linear combination of standards, and the amount obtained from electrochemical characterization based on measured capacity was achieved. The electrochemical mechanism in all studied batteries was confirmed to be a reduction of double carbonyl bond and the intermediate anion was identified with the help of theoretical calculations. X-ray Raman spectroscopy of the oxygen K-edge was shown to be a viable characterization technique for accurate tracking of the redox reaction inside metal-organic batteries., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Human hair absorbs numerous biomolecules from the body during its growth. This can act as a fingerprint to determine substance intake of an individual, which can be useful in forensic studies. The cocaine concentration profile along the growth axis of hair indicates the time evolution of the metabolic incorporation of cocaine usage. It could be either assessed by chemical extraction and further analysis of hair bundels, or by direct single hair fibre analysis with mass spectroscopy imaging (MSI). Within this work, we analyzed the cocaine distribution in individual hair samples using MeV-SIMS. Unlike conventional surface analysis methods, we demonstrate high yields of nonfragmented molecular ions from the surface of biological materials, resulting in high chemical sensitivity and non-destructive characterisation. Hair samples were prepared by longitudinally cutting along the axis of growth, leaving half-cylindrical shape to access the interior structure of the hair by the probing ion beam, and attached to the silicon wafer. A focused 5.8 MeV 35Cl6+ beam was scanned across the intact, chemically pristine hair structure. A non-fragmented protonated [M+ H]+ cocaine molecular peak at m/z = 304 was detected and localized along the cross-section of the hair. Its intensity exhibits strong fluctuations along the direction of the hair's growth, with pronounced peaks as narrow as 50 micrometres, corresponding to a metabolic incorporation time of approx. three hours., Competing Interests: The authors have declared that no competing interests exist.

In a lithium/sulfur (Li/S) battery, the reduction of sulfur during discharge involves a particular mechanism, where the active material successively dissolves into the electrolyte to form lithium polysulfide intermediate species (Li 2 S x ), with x being a function of the state of charge. In this work, sulfur K-edge resonant inelastic X-ray scattering measurements were performed for the characterization of different Li 2 S x polysulfide standard solutions. High-energy resolution fluorescence detected X-ray absorption spectroscopy allowed clear separation the pre-edge absorption peak corresponding to terminal sulfur atoms from the main absorption peak due to internal atoms and allowed quantitative evaluation of the evolution of the peak area ratio as a function of the polysulfide chain length. Results of this experimental work demonstrate that the normalized area of the pre-edge is a reliable fingerprint of the Li 2 S x mean chain length in agreement with recent theoretical predictions. As a perspective, this work confirms that operando HERFD XAS can be used to differentiate mean polysulfide composition, which is key issue in the characterization of Li/S cells.

We report an electron scattering experiment on argon gas where a keV electron beam is used as a probe and electrons are collected with a magnetic bottle spectrometer. For this purpose, we have built a thermionic gun that produces electron pulses with nanosecond duration by sweeping the beam across a small aperture. To reach the target, electrons must pass through the hole in an axially symmetric arrangement of strong permanent magnets required to operate the magnetic bottle. From the recorded multi-hit sequence of electron arrival times on the microchannel plate detector, a kinetic energy spectrum is built that allows an analysis of the elastic and inelastic electron scattering channels by means of the coincidence technique. After a description of the instrumental configuration and discussion of suitable working parameters, the results of an angle-integrated (e, 2e) experiment are presented for 800 eV electron scattering on argon atoms.

Single-site Double-Core Hole (ss-DCH or K -2 ) and two-site Double-Core Hole (ts-DCH or K -1 K -1 ) photoelectron spectra including satellite lines were experimentally recorded for the aromatic C 6 H 6 molecule using the synchrotron radiation and multielectron coincidence technique. Density functional theory and post-Hartree-Fock simulations providing binding energies and relative intensities allow us to clearly assign the main K -2 line and its satellites. K -1 K -1 states' positions and assignments are further identified using a core-equivalent model. We predict that, contrary to what has been observed in the C 2 H 2n series of molecules, the K -1 K -1 energy-level ordering in C 6 H 6 does not reflect the core-hole distances between the two holes.

Photon-induced fragmentation of a full set of chlorinated methanes (CH 3 Cl, CH 2 Cl 2 , CHCl 3 , CCl 4 ) has been investigated both experimentally and computationally. Using synchrotron radiation and electron-ion coincidence measurements, the dissociation processes were studied after chlorine 2p electron excitation. Experimental evidence for CH 3 Cl and CH 2 Cl 2 contains unique features suggesting that fast dissociation processes take place. By contrast, CHCl 3 and CCl 4 molecules do not contain the same features, hinting that they experience alternative mechanisms for dissociation and charge migration. Computational work indicates differing rates of charge movement after the core-excitation, which can be used to explain the differences observed experimentally.

A combination of resonant inelastic x-ray scattering and resonant Auger spectroscopy provides complementary information on the dynamic response of resonantly excited molecules. This is exemplified for CH_{3}I, for which we reconstruct the potential energy surface of the dissociative I 3d^{-2} double-core-hole state and determine its lifetime. The proposed method holds a strong potential for monitoring the hard x-ray induced electron and nuclear dynamic response of core-excited molecules containing heavy elements, where ab initio calculations of potential energy surfaces and lifetimes remain challenging.

We report results of analysis of a month-long measurement of indoor air and environment quality parameters in one gym during sporting activities such as football, basketball, volleyball, badminton, boxing, and fitness. We have determined an average single person's contribution to the increase of temperature, humidity, and dust concentration in the gym air volume of 12500 m(3) : during 90-min exercise performed at an average heart rate of 143 ± 10 bpm, a single person evaporated 0.94 kg of water into the air by sweating, contributed 0.03 K to the air temperature rise and added 1.5 μg/m(3) and 5 ng/m(3) to the indoor concentration of inhalable particles (PM10 ) and Ca concentration, respectively. As the breathing at the observed exercise intensity was about three times faster with respect to the resting condition and as the exercise-induced PM10 concentration was about two times larger than outdoors, a sportsman in the gym would receive about a sixfold higher dose of PM10 inside than he/she would have received at rest outside., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

We present a theoretical and experimental study of resonant inelastic x-ray scattering on a large group of chlorinated hydrocarbons: CH3Cl, CH2Cl2, CHCl3, CCl4, CH3CH2Cl, ClCH2CH2Cl, CH3CHCl2, CH3CCl3, C2H2Cl2-iso, C2H2Cl2-cis, C2H2Cl2-trans, and C6H5Cl. Differences in structural and dynamical properties of the molecules generated by diverse chemical environments are observed in the measured Cl(K(α)) spectral maps as well as in the Cl(K) total fluorescence yield spectra. The energy position, relative intensity, and the width of the Franck-Condon distribution of low-lying σ* and π* resonances are extracted by a fitting procedure taking into account the experimental broadening. The theoretical values obtained with the transition potential and Δ Kohn-Sham methods are in good agreement with the experimental parameters indicating subtle differences due to variations in the molecular structure.

In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range.

An experimental and theoretical study of phosphorus electronic structure based on high energy resolution X-ray emission spectroscopy was performed. The Kα and Kβ emission spectra of several phosphorus compounds were recorded using monochromatic synchrotron radiation and megaelectronvolt (MeV) proton beam for target excitation. Measured spectra are compared to the results of ab initio quantum chemical calculations based on density functional theory (DFT). Clear correlation between energy position of the Kα emission line and the phosphorus formal oxidation state as well as DFT-calculated number of valence electrons is obtained; measured energy shifts are reproduced by the calculations. Chemical sensitivity is increased further by looking at the Kβ emission spectra probing directly the structure of occupied molecular orbitals. Energies and relative intensities of main components are given together with the calculated average atomic character of the corresponding molecular orbitals involved in transitions.

We present in detail a theoretical model that provides absolute cross sections for simultaneous core-ionization core-excitation (K(-2)V) and compare its predictions with experimental results obtained on the water molecule after photoionization by synchrotron radiation. Two resonances of different symmetries are assigned in the main K(-2)V peak and comparable contributions from monopolar (direct shake-up) and dipolar (conjugate shake-up) core-valence excitations are identified. The main peak is observed with a much greater width than the total experimental resolution. This broadening is the signature of nuclear dynamics.

The formalism developed in the companion Paper I is used here for the interpretation of spectra obtained recently on the nitrogen molecule. Double core-hole ionization K(-2) and core ionization-core excitation K(-2)V processes have been observed by coincidence electron spectroscopy after ionization by synchrotron radiation at different photon energies. Theoretical and experimental cross sections reported on an absolute scale are in satisfactory agreement. The evolution with photon energy of the relative contribution of shake-up and conjugate shake-up processes is discussed. The first main resonance in the K(-2)V spectrum is assigned to a K(-2)π(∗) state mainly populated by the 1s→ lowest unoccupied molecular orbital dipolar excitation, as it is in the K(-1)V NEXAFS (Near-Edge X-ray Absorption Fine Structure) signals. Closer to the K(-2) threshold Rydberg resonances have been also identified, and among them a K(-2)σ(∗) resonance characterized by a large amount of 2s/2p hybridization, and double K(-2)(2σ(∗)/1π/3σ)(-1)1π(∗2) shake-up states. These resonances correspond in NEXAFS spectra to, respectively, the well-known σ(∗) shape resonance and double excitation K(-1)(2σ(∗)/1π/3σ)(-1)1π(∗2) resonances, all being positioned above the threshold.

Seeded free electron lasers theoretically have the intensity, tunability, and resolution required for multiphoton spectroscopy of atomic and molecular species. Using the seeded free electron laser FERMI and a novel detection scheme, we have revealed the two-photon excitation spectra of dipole-forbidden doubly excited states in helium. The spectral profiles of the lowest (-1,0)(+1) (1)S(e) and (0,1)(0) (1)D(e) resonances display energy shifts in the meV range that depend on the pulse intensity. The results are explained by an effective two-level model based on calculated Rabi frequencies and decay rates.

We report a theoretical and experimental study of the high resolution resonant K(α) X-ray emission lines around the chlorine K-edge in gas phase 1,1-dichloroethylene. With the help of ab initio electronic structure calculations and cross section evaluation, we interpret the lowest lying peak in the X-ray absorption and emission spectra. The behavior of the K(α) emission lines with respect to frequency detuning highlights the existence of femtosecond nuclear dynamics on the dissociative Potential Energy Surface of the first K-shell core-excited state.

A theoretical analysis of dissociation dynamics of chlorine K-σ(*) core-excited molecules is performed. The potential energy surfaces of HCl, Cl2, CH3Cl, CH2Cl2, CHCl3, CCl4, CFCl3, CF2Cl2, and CF3Cl are calculated along the normal vibrational modes of the ground electronic state yielding the widths of the corresponding Franck-Condon distributions. An insight into the potential energy surface of 1st σ(*) resonances shows that the initial dissociation dynamics of chloro(fluoro)methanes mainly involves the distancing of the carbon and the core-excited chlorine atom and is practically independent of other atoms in the molecule, which is in agreement with the recent experimental findings. The carbon atom pulls out the remaining three atoms shortly after piercing the three-atom plane resulting in a high vibrationally excited state of the fragment if the reconnection time is smaller than the lifetime of the L shell.

The dissociation process following the Cl K-shell excitation to σ* resonances is studied by high resolution spectroscopy of resonant elastic and inelastic x-ray scattering on CH3Cl, CH2Cl2, CHCl3, and CCl4 molecules. Calculations employing the transition potential and Delta-Kohn-Sham DFT approach are in good agreement with the measured total fluorescence yield and show the presence of a second quasidegenerate group of states with σ* character above the lowest σ* unoccupied molecular orbital for molecules with more than one Cl atom. A bandwidth narrowing and a nonlinear dispersion behavior is extracted from the Kα spectral maps for both σ* resonances. The fitted data indicate that the widths of the Franck-Condon distributions for the first and second σ* resonances are comparable for all the molecules under study. In addition, an asymmetric broadening of the emission peaks is observed for resonant elastic x-ray scattering with zero detuning on both σ* resonances. This is attributed to the fast dissociation, transferring about 0.15 of the scattering probability into higher vibrational modes.

We have investigated a local chemical environment effect on Auger spectra of ethyl trifluoroacetate (C(4)H(5)F(3)O(2)), using multi-electron coincidence spectroscopy and high-resolution electron spectroscopy. Site-specific KVV Auger spectra for each carbon atom, and for the fluorine and oxygen atoms are presented. The extent of hole localization in the final dicationic states was investigated with the help of theoretical calculations based on a two-hole population analysis. The Auger spectra have been simulated using a statistical approach. It is found that all Auger decays populate mainly localized dicationic states, with the two holes located either on the same fluorine atom or on adjacent fluorine atoms. While the decay of the F 1s hole populates exclusively the former states, the latter class of states is also populated by the decay of the C and O 1s holes.

The electrical resistivity of amorphous Fe(100-x)Zr(x) metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe(100-x)Zr(x) alloys.

The background induced by the members of the thorium decay sequence in six high-resolution, gamma-ray spectrometers was analyzed. For the analysis, the count rates in the peaks of the background spectra, normalized to the unit of emission probability and detection probability, were used. The energy dependence of these normalized count rates carries information about the location of the sources of contamination. The contributions of the detector contamination, the contamination of the shielding material and the radiation penetrating the shield were calculated. The comparison of these contributions among the spectrometers pointed to the weaknesses of some shields, making such a comparison a useful tool for assessing the effectiveness of the shields., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

A complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry has been constructed for a 2-6 keV energy range with sub natural line-width energy resolution. The spectrometer is designed to measure x-ray emission induced by photon and charged particle impact on solid and gaseous targets. It works with a relatively large x-ray source placed inside the Rowland circle and employs position sensitive detection of diffracted x-rays. Its compact modular design enables fast and easy installation at a synchrotron or particle accelerator beamline. The paper presents main characteristics of the spectrometer and illustrates its capabilities by showing few selected experimental examples.

We present measurements of the resonant inelastic x-ray scattering (RIXS) spectra of the CH(3)I molecule in the hard-x-ray region near the iodine L(2) and L(3) absorption edges. We show that dispersive RIXS spectral features that were recognized as a fingerprint of dissociative molecular states can be interpreted in terms of ultrashort natural lifetime of ∼200 attoseconds in the case of the iodine L-shell core-hole. Our results demonstrate the capacity of the RIXS technique to reveal subtle dynamical effects in molecules with sensitivity to nuclear rearrangement on a subfemtosecond time scale.

The formation of hollow molecules (with a completely empty K shell in one constituent atom) through single-photon core double ionization has been demonstrated using a sensitive magnetic bottle experimental technique combined with synchrotron radiation. Detailed properties are presented such as the spectroscopy, formation, and decay dynamics of the N(2)(2+) K(-2) main and satellite states and the strong chemical shifts of double K holes on an oxygen atom in CO, CO2, and O2 molecules.