Search

International audience; We propose a novel approach for an indirect probing of conjugation and hyperconjugation in coreexcited molecules using resonant Auger spectroscopy. Our work demonstrates that the changes in the electronic structure of thiophene (C 4 H 4 S) and thiazole (C 3 H 3 NS), occurring in the process of resonant sulfur K-shell excitation and Auger decay, affect the stabilisation energy resulting from π−conjugation and hyperconjugation. The variations in the stabilisation energy manifest themselves in the resonant S KL 2,3 L 2,3 Auger spectra of thiophene and thiazole. The comparison of the results obtained for the conjugated molecules and for thiolane (C 4 H 8 S), the saturated analogue of thiophene, has been performed. The experimental observations are interpreted using high-level quantum-mechanical calculations and the natural bond orbital analysis.

Fragmentation dynamics of core-excited isolated ammonia molecules is studied by two different and complementary experimental methods, high-resolution resonant Auger spectroscopy and electron energy-selected Auger electron–photoion coincidence spectroscopy (AEPICO). The combined use of these two techniques allows obtaining information on different dissociation patterns, in particular fragmentation before relaxation, often called ultrafast dissociation (UFD), and fragmentation after relaxation. The resonant Auger spectra contain the spectral signature of both molecular and fragment final states, and therefore can provide information on all events occurring during the core-hole lifetime, in particular fragmentation before relaxation. Coincidence measurements allow correlating Auger electrons with ionic fragments from the same molecule, and relating the ionic fragments to specific Auger final electronic states, and yield additional information on which final states are dissociative, and which ionic fragments can be produced in timescales either corresponding to the core-hole lifetime or longer. Furthermore, we show that by the combined use of two complementary experimental techniques we are able to identify more electronic states of the NH2+ fragment with respect to the single one already reported in the literature.

The photochemically induced ring-opening isomerization reaction of 1,3-cyclohexadiene to 1,3,5-hexatriene is a textbook example of a pericyclic reaction and has been amply investigated with advanced spectroscopic techniques. The main open question has been the identification of the single reactive state which drives the process. The generally accepted description of the isomerization pathway starts with a valence excitation to the lowest lying bright state, followed by a passage through a conical intersection to the lowest lying doubly excited state, and finally a branching between either the return to the ground state of the cyclic molecule or the actual ring-opening reaction leading to the open-chain isomer. Here, in a joint experimental and computational effort, we demonstrate that the evolution of the excitation–deexcitation process is much more complex than that usually described. In particular, we show that an initially high-lying electronic state smoothly decreasing in energy along the reaction path plays a key role in the ring-opening reaction.

We study vibrationally-resolved resonant Auger (RAS) spectra of ammonia recorded in coincidence with the NH2+ fragment, which is produced in the course of dissociation either in the core-excited 1s−14a11 intermediate state or the first spectator 3a−24a11 final state. Correlation of the NH2+ ion flight times with electron kinetic energies allows directly observing the Auger-Doppler dispersion for each vibrational state of the fragment. The median distribution of the kinetic energy release EKER, derived from the coincidence data, shows three distinct branches as a function of Auger electron kinetic energy Ee: Ee + 1.75EKER = const for the molecular band; EKER = const for the fragment band; and Ee + EKER = const for the region preceding the fragment band. The deviation of the molecular band dispersion from Ee + EKER = const is attributed to the redistribution of the available energy to the dissociation energy and excitation of the internal degrees of freedom in the molecular fragment. We found that for each vibrational line the dispersive behavior of EKERvs. Ee is very sensitive to the instrumental uncertainty in the determination of EKER causing the competition between the Raman (EKER + Ee = const) and Auger (Ee = const) dispersions: increase in the broadening of the finite kinetic energy release resolution leads to a change of the dispersion from the Raman to the Auger one.

Journal of physics / B 55(1), 014001 (2022). doi:10.1088/1361-6455/ac489d, The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH$_2$BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump���XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH$_2$Br radicals produced by C���I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH$_2$BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way., Published by IOP Publ., Bristol

In molecular photoemission, the analogue of the celebrated Young's double slit experiment is coherent electron emission from two equivalent atomic centers, giving rise to an interference pattern. Here multi-slit interference is investigated in inner-valence photoionization of propane, n- butane, isobutane and methyl peroxide. A more complex pattern is observed due to molecular orbital delocalization in polyatomic molecules, blurring the distinction between interference and diffraction. The potential to extract geometrical information is emphasized, as a more powerful extension of the EXAFS technique. Accurate reproduction of experimental features is obtained by simulations at the static Density Functional Theory level.

The photoionization branching ratios of spin–orbit doublets are studied both experimentally and theoretically at energies several keV above threshold. The results show significant relativistic effects for Ar 2p in the autoionizing region below the 1s threshold, and large many-body effects for Xe 3d and 4d in the vicinity of the L-shell thresholds. The branching ratios in Xe are also found to vary significantly over very broad multi-keV energy regions both above and below the inner-shell thresholds. In addition, the Ar 2p study confirms experimentally the decades-old theoretical prediction that the nonresonant branching ratio does not approach the statistical (nonrelativistic) value, and, in fact, progressively diverges from statistical with increasing photon energy.

We have built an x-ray spectrometer in a von Hamos configuration based on a highly annealed pyrolytic graphite crystal. The spectrometer is designed to measure x-ray emission in the range of 2���5 keV. A spectral resolution E/��E of 4000 was achieved by recording the elastic peak of photons issued from the GALAXIES beamline at the SOLEIL synchrotron radiation facility.

International audience; Using synchrotron radiation in the tender X-ray regime, a photoelectron spectrum showing the formation of single site double-core-hole pre-edge states, involving the K shell of the O atom in CO, has been recorded by means of high-resolution electron spectroscopy. The experimentally observed structures have been simulated, interpreted and assigned, employing state-of-the-art ab initio quantum chemical calculations, on the basis of a theoretical model, accounting for their so-called direct or conjugate character. Features appearing above the double ionization threshold have been reproduced by taking into account the strong mixing between multi-excited and continuum states. The shift of the σ* resonance below the double ionization threshold, in combination with the non-negligible contributions of multi-excited configurations in the final states reached, gives rise to a series of avoided crossings between the different potential energy curves.

State-of-the-art argon $KLL$ Auger spectra measured using photon energies of $h\ensuremath{\nu}=3216$ and 3400 eV are presented along with an Ar $[1s]$ photoelectron spectrum (square brackets indicate holes in the respective orbital). The two different photon energies used for measuring the Auger spectra allow distinguishing between the shake transitions during the Auger decay and the Auger transitions of the photoelectron satellites. A complete assignment of satellite transitions is provided, partially based on configuration-interaction calculations. In addition, Ar $[1s3(s,p)]{n}^{\ensuremath{'}}{l}^{\ensuremath{'}}\ensuremath{\rightarrow}[2{p}^{2}{(}^{1}{D}_{2})]$ transitions are observed, which can be explained by knock-down transitions leading to a direct exchange of angular momentum between the excited electron and the Auger electron. The lifetime broadenings of the Ar $[2s]$ single-core-hole state and the $[2{s}^{2}]$ and $[2s2p]$ double-core-hole states are also determined, confirming previously observed trends for double-core-hole states.

A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at ≅13.482 keV is reported. In detail, the Br 1s-1 X-ray absorption spectrum, the 1s-1 photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s-1 ionization energy as well as on top of the Br 1s-1σ* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s-1 core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s-1 single core-hole state as well as of the Br(2s-2,2s-12p-1,2p-2) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p-2σ* potential energy curve is found to be about -13.60 eV Å-1. The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br.

We present a combined experimental and theoretical study of the double-core-hole photoelectron spectrum obtained in isolated water molecules irradiated with hard x-rays above the oxygen K −2 threshold. States of the type O K −2 V and multiply excited states are created by single-photon absorption and subsequent one-electron emission. A detailed analysis enabled by high experimental resolution reveals dissociative nuclear dynamics in the K −2 V pre-edge states. At the binding energies above the K −2 double-ionization potential, a complex spectral pattern is observed and attributed to highly excited states involving multiple shake-up excitation processes with the aid of state-of-the-art theoretical calculations. A strong broadening due to the nuclear motion indicates a highly dissociative nature of these multiply excited states, in agreement with the theoretical analysis.

We present here a review of the most significant recent achievements in the field of HAXPES (HArd X-ray PhotoElectron Spectroscopy) on isolated atoms and molecules, and related spectroscopies. The possibility of conducting hard x-ray photoexcitation and photoionization experiments under state-of-the art conditions in terms of photon and electron kinetic energy resolution has become available only in the last few years. HAXPES has then produced structural and dynamical information at the level of detail already reached in the VUV and soft-x-ray ranges. The much improved experimental conditions have allowed extending to the hard x-ray range some methods well established in soft x-ray spectroscopies. Investigations of electron and nuclear dynamics in the femtosecond (fs, 10-15 sec) and even attosecond (as, 10-18 sec) regime have become feasible. Complex relaxation phenomena following deep-core ionization can now be enlightened in great detail. Other phenomena like e.g. recoil-induced effects are much more important in fast photoelectron emission, which can be induced by hard x-rays. Furthermore, a new kind of ionic states with double core holes can be observed by x-ray single-photon absorption. Future perspectives are also discussed.

A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at approximately equal to 13.482 keV is reported. In detail, the Br 1s(-1) X-ray absorption spectrum, the 1s(-1) photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s(-1) ionization energy as well as on top of the Br 1s(-1)sigma* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s(-1) core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s(-1) single core-hole state as well as of the Br(2s(-2),2s(-1)2p(-1),2p(-2)) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p(-2)sigma* potential energy curve is found to be about -13.60 eV angstrom(-1). The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br.

We investigate the multiphoton ionization of NO2 using tunable (430-375 nm) femtosecond pulses and photoelectron-photoion coincidence momentum spectroscopy. In order to understand the complex electronic and nuclear photodynamics at play following absorption of three to five photons, we also report extended photoionization calculations using correlated targets and coupled channels. Exploring the multiphoton dissociative ionization (MPDI) and multiphoton ionization (MPI) processes over such a broad energy range enables us to lend further support to our work carried out around 400 nm of a femtosecond laser [S. Marggi Poullain et al., J. Phys. B: At., Mol. Opt. Phys., 2014, 47, 124024]. Two excitation energy regions are identified and discussed in terms of the proposed reaction pathways, highlighting the significant role of Rydberg states, such as the [R*(6a1)-1, 3pσ] Rydberg state, in the NO2 multiphoton excitation and photoionization. These new results support our previous assumption that different bent and linear geometries of the NO2+(X1Σg) ionic state contribute to the MPDI and MPI, consistent with the reported calculations which reveal an important vibronic coupling characterizing the photoemission. Remarkably, the strong anisotropy of the recoil frame photoelectron angular distribution (RFPAD) previously observed at 400 nm appears as a fingerprint across the whole explored photon energy range.

Differences in postcollision interaction (PCI) effects on Kr L_{3}M_{4,5}M_{4,5} Auger electron spectra were observed, depending on whether the initial photoionization occurred slightly above the K threshold or slightly above the L_{3} threshold. For the former, KL fluorescence emission most likely happens and then Auger processes due to the L_{3} hole follow. The time delay due to fluorescence causes a reduced shift of the Auger peak and tailing toward lower energy, since the Auger overtaking of the photoelectron happens later in time and at a location farther away from the ionic core, compared to the case for the simple one-step L_{3}M_{4,5}M_{4,5} Auger decay after L-shell photoionization. Time-dependent theory for PCI in multistep processes agrees well with experiment, illustrating the effect as an internal clock for the time-sequence of the dynamical process.

Electron-ion coincidence experimental data obtained following argon 1s photoionization are reported. Slow photoelectrons were measured in coincidence with Ar+ and Ar2+ ions, and the beta angular di ...

The Si 1s−1, Si 2s−1, and Si 2p−1 photoelectron spectra of the SiX4 molecules with X = F, Cl, Br, CH3 were measured. From these spectra the Si 1s−1 and Si 2s−1 lifetime broadenings were determined, revealing a significantly larger value for the Si 2s−1 core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is in line with the results of the Si 2p−1 core holes of a number of SiX4 molecules, with an exceptionally large broadening for SiF4. For the Si 2s−1 core hole of SiF4 the difference to the other SiX4 molecules can be explained in terms of Interatomic Coulomb Decay (ICD)-like processes. For the Si 2p−1 core hole of SiF4 the estimated values for the sum of the Intraatomic Auger Electron Decay (IAED) and ICD-like processes are too small to explain the observed linewidth. However, the results of the given discussion render for SiF4 significant contributions from Electron Transfer Mediated Decay (ETMD)-like processes at least plausible. On the grounds of our results, some more molecular systems in which similar processes can be observed are identified.

The Si 1s-1, Si 2s-1, and Si 2p-1 photoelectron spectra of the SiX4 molecules with X = F, Cl, Br, CH3 were measured. From these spectra the Si 1s-1 and Si 2s-1 lifetime broadenings were determined, revealing a significantly larger value for the Si 2s-1 core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is in line with the results of the Si 2p-1 core holes of a number of SiX4 molecules, with an exceptionally large broadening for SiF4. For the Si 2s-1 core hole of SiF4 the difference to the other SiX4 molecules can be explained in terms of Interatomic Coulomb Decay (ICD)-like processes. For the Si 2p-1 core hole of SiF4 the estimated values for the sum of the Intraatomic Auger Electron Decay (IAED) and ICD-like processes are too small to explain the observed linewidth. However, the results of the given discussion render for SiF4 significant contributions from Electron Transfer Mediated Decay (ETMD)-like processes at least plausible. On the grounds of our results, some more molecular systems in which similar processes can be observed are identified.

International audience; We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range allows us to study and disentangle shake processes and intramolecular inelastic scattering effects. In this gas-phase study, relative intensities of the carbon 1s photoelectron lines from chemically inequivalent carbon atoms in the same molecule have been measured as a function of the incident photon energy in the range of 300–6000 eV. We present relative cross sections for the chemically shifted carbon 1s lines in the photoelectron spectra of ethyl trifluoroacetate (the “ESCA” molecule). The results are compared with those of methyl trifluoroacetate and S-ethyl trifluorothioacetate as well as a series of chloro-substituted ethanes and 2-butyne. In the soft X-ray energy range, the cross sections show an extended X-ray absorption fine structure type of wiggles, as was previously observed for a series of chloroethanes. The oscillations are damped in the hard X-ray energy range, but deviations of cross-section ratios from stoichiometry persist, even at high energies. The current findings are supported by theoretical calculations based on a multiple scattering model. The use of soft and tender X-rays provides a more complete picture of the dominant processes accompanying photoionization. Such processes reduce the main photoelectron line intensities by 20–60%. Using both energy ranges enabled us to discern the process of intramolecular inelastic scattering of the outgoing electron, whose significance is otherwise difficult to assess for isolated molecules. This effect relates to the notion of the inelastic mean free path commonly used in photoemission studies of clusters and condensed matter.

The 1s −2 Auger hypersatellite spectrum of argon is studied experimentally and theoretically. In total, three transitions to the final states 1s −12p −2(2 S e ,2 D e ) and 1s −12s −1(1 S)2p −1(2 P o ) are experimentally observed. The lifetime broadening of the 1s −2 → 1s −12p −2(2 S e ,2 D e ) states is determined to be 2.1(4) eV. For the used photon energy of hν = 7500 eV a KK/K ionisation ratio of 2.5(3) × 10−4 is derived. Generally, a good agreement between the experimental and present theoretical energy positions, linewidths, and intensities is obtained.

Synopsis We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range extending to hard x-rays allows studying and disentangling shake processes and intramolecular inelastic scattering effects. An “EXAFS”-type of oscillatory behaviour of the relative C 1s cross sections is observed in a wide photon energy range up to 1 keV due to multiple intramolecular elastic scattering of the photoelectron. These effects are also present in solids and constitute a significant part of all elastic and inelastic scattering effects occurring in solids.

The photodissociation dynamics of CH

We present a combined experimental and theoretical study of the Auger-emission spectrum following double core ionization and excitation of gas-phase water molecules with hard-x-ray synchrotron radiation above the O $K^{−2}$ threshold. We observe an indication of ultrafast proton motion occurring within the 1.5 fs lifetime of the double-core-hole (DCH) states in water. Furthermore, we have identified symmetric and antisymmetric dissociation modes characteristic for particular DCH states. Our results serve as a fundamental reference for state-of-the-art studies of DCH dynamic processes in liquid water both at synchrotron and free-electron-laser facilities.

A mixture of ${\mathrm{CF}}_{4}$ and CO gases is used to study photoelectron recoil effects extending into the tender x-ray region. In ${\mathrm{CF}}_{4}$, the vibrational envelope of the C $1s$ photoelectron spectrum becomes fully dominated by the recoil-induced excitations, revealing vibrational modes hidden from Franck-Condon excitations. In CO, using ${\mathrm{CF}}_{4}$ as an accurate energy calibrant, we determine the partitioning of the recoil-induced internal excitation energy between rotational and vibrational excitation. The observed rotational recoil energy is 2.88(28) times larger than the observed vibrational recoil energy, well in excess of the ratio of 2 predicted by the basic recoil model. The experiment is, however, in good agreement with the value of 2.68 if energy transfer via Coriolis coupling is included.

Complex decay pathways involving radiative and nonradiative relaxation after deep core-level ionization in argon are disentangled by a unique combination of several synchrotron radiation-based spectroscopic techniques. In particular, by comparing the results obtained from electron-ion coincidence, photon-ion coincidence, and x-ray emission measurements, we are able to distinguish the final ionic states produced in the cascade decay involving Kα and Kβ radiative decay and final ionic states produced by nonradiative cascade decay. High-resolution Auger electron spectroscopy is then used as a complementary tool to identify the LMM transitions contributing to the cascade decay. Ab initio calculations are performed to identify the electronic states involved in the LMM decay.

The formation of double core hole pre-edge states of the form 1s-12p-1(1,3P)σ*,nl for HCl, located on the binding energy scale as deep as 3 keV, has been investigated by means of a high resolution single channel electron spectroscopy technique recently developed for the hard X-ray region. A detailed spectroscopic assignment is performed based on ab initio quantum chemical calculations and by using a sophisticated fit model comprising regular Rydberg series. Quantum defects for the different Rydberg series are extracted and the energies for the associated double core hole ionization continua are extrapolated. Dynamical information such as the lifetime width of these double-core-hole pre-edge states and the slope of the related dissociative potential energy curves are also obtained. In addition, 1s-12p-1V-1nlλn'l'λ' double shake-up transitions and double core hole states of the form 1s-12s-1(1,3S)σ*,4s are observed.

The journal of chemical physics 149(20), 204313 (2018). doi:10.1063/1.5041381, The photodissociation dynamics of CH$_3$I and CH$_2$ClI at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815 nm probe pulse. Fragment ion momenta over a wide m/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH$_2$ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion., Published by American Institute of Physics, Melville, NY

Fragmentation processes following C $1s\ensuremath{\rightarrow}\text{lowest}$ unoccupied molecular orbital core excitations in ${\mathrm{CF}}_{4}$ have been analyzed on the ground of the angular distribution of the ${\mathrm{CF}}_{3}^{+}$ emitted fragments by means of Auger electron-photoion coincidences. Different time scales have been enlightened, which correspond to either ultrafast fragmentation, on the few-femtosecond scale, where the molecule has no time to rotate and the fragments are emitted according to the maintained orientation of the core-excited species, or dissociation after resonant Auger decay, where the molecule still keeps some memory of the excitation process before reassuming random orientation. Potential energy surfaces of the ground, core-excited, and final states have been calculated at the ab initio level, which show the dissociative nature of the neutral excited state, leading to ultrafast dissociation, as well as the also dissociative nature of some of the final ionic states reached after resonant Auger decay, yielding the same fragments on a much longer time scale.

The dynamics following laser-induced molecular photodissociation of gas-phase CH2BrI at 271.6 nm were investigated by time-resolved Coulomb-explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH2BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of CH2Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb-explosion imaging as a real-time probe of chemical dynamics.

A concrete mechanism of angular-momentum transfer in photoionization process is proposed for electron photoemission from deep inner atomic shells. It is demonstrated that the leading contribution to angular-momentum transfer is provided by postcollision interaction of the photoelectrons and Auger electrons. The standard theoretical approach to postcollision interaction has been considerably improved by taking into account angular-momentum transfer. The theory developed is applied to the photoionization of $1{s}^{2}$ shell in Ar. Calculations show the noticeable influence of angular-momentum transfer on the photoelectron angular distribution.

We present the hypersatellite Auger spectrum of neon which contains the decay transitions of the ${K}^{\ensuremath{-}2}, {K}^{\ensuremath{-}2}V, {K}^{\ensuremath{-}2}{L}^{\ensuremath{-}1}, {K}^{\ensuremath{-}2}{L}^{\ensuremath{-}1}V$, and ${K}^{\ensuremath{-}1}{L}^{\ensuremath{-}1}V$ states. The Auger decays of these types of core-hole states show different line shapes and linewidths which can be distinguished due to the high experimental resolution available for the present experiments. The individual Auger transitions are assigned based on various approaches. Complementary calculations are performed to assign the ${K}^{\ensuremath{-}2}{L}^{\ensuremath{-}1}\ensuremath{\rightarrow}{K}^{\ensuremath{-}1}{L}^{\ensuremath{-}3}$ and the ${K}^{\ensuremath{-}2}{L}^{\ensuremath{-}1}V\ensuremath{\rightarrow}{K}^{\ensuremath{-}1}{L}^{\ensuremath{-}3}V$ Auger transitions. Based on the obtained results we were able to derive the ratio for the double to single ionization yield.

International audience; 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 CH3I, 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 present a comprehensive experimental and theoretical investigation on the LMM, LMN, and LNN normal Auger spectra of xenon, which reveal excellent agreement with theory when core-hole lifetimes of the two-hole final states are taken into account. Generally, the spectra turned out to be highly complex due to a strong overlap of the Auger transitions subsequent to 2s(1/2)(-1), 2p(1/2)(-1), and 2p(3/2)(-1) ionization. This overlap is due to the splitting of the three initial L core holes and the different final M and N core holes being on the same order of magnitude of several hundred eV. The Auger transitions are assigned in detail based on the theoretical results. Most of the MM, MN, and NN final states are described well based on jj coupling. In addition, we present a detailed assignment of the resonant LM45M45 Auger transition subsequent to the 2s -> 6p, 7p and 2p -> 5d, 6d excitations.

International audience; Tuning hard x-ray excitation energy along Cl 1s→σ∗ resonance in gaseous HCl allows manipulating molecular fragmentation in the course of the induced multistep ultrafast dissociation. The observations are supported by theoretical modeling, which shows a strong interplay between the topology of the potential energy curves, involved in the Auger cascades, and the so-called core-hole clock, which determines the time spent by the system in the very first step. The asymmetric profile of the fragmentation ratios reflects different dynamics of nuclear wave packets dependent on the photon energy.

We report on the newly operational HAXPES endstation located on the GALAXIES beamline of the SOLEIL French synchrotron facility. The photon energy provided by the beamline covers the 2.4–12 keV range, and electrons of kinetic energy up to 12 keV can be analyzed. The HAXPES station is comprised of a UHV analysis chamber designed for investigating both solid samples and gases for the first time at high kinetic energy, and a fully equipped preparation chamber. We present the first results of X-ray photoemission and photoabsorption collected with this setup.

The unique capabilities of resonant inelastic X-ray scattering (RIXS) to provide a deep insight into molecular dynamics following core excitation are reviewed here. Characteristic features of molec ...

Using synchrotron radiation and high-resolution electron spectroscopy, we have directly observed and identified specific photoelectrons from K^{-2}V states in neon corresponding to simultaneous 1s ionization and 1s→valence excitation. The natural lifetime broadening of the K^{-2}V states and the relative intensities of different types of shakeup channels have been determined experimentally and compared to ab initio calculations. Moreover, the high-energy Auger spectrum resulting from the decay of Ne^{2+}K^{-2} and Ne^{+}K^{-2}V states as well as from participator Auger decay from Ne^{+}K^{-1}L^{-1}V states, has been measured and assigned in detail utilizing the characteristic differences in lifetime broadenings of these core hole states. Furthermore, post collision interaction broadening of Auger peaks is clearly observed only in the hypersatellite spectrum from K^{-2} states, due to the energy sharing between the two 1s photoelectrons which favors the emission of one slow and one fast electron.

We have studied the ${K}^{\ensuremath{-}2}V$ process corresponding to simultaneous $K$-shell ionization and $K$-shell excitation in the $\mathrm{C}{\mathrm{O}}_{2}$ molecule. We define these ${K}^{\ensuremath{-}2}V$ states as super shake-up, at variance with the ``conventional'' ${K}^{\ensuremath{-}1}{v}^{\ensuremath{-}1}V$ shake-up states. While the nature and evolution with photon energy of the conventional shake-up satellites has been the object of many studies, no such data on a large photon-energy range were previously reported on super shake-up. The $\mathrm{C}{\mathrm{O}}_{2}$ molecule is a textbook example because it exhibits two well-isolated ${K}^{\ensuremath{-}2}V$ resonances (with V being $2{\ensuremath{\pi}}_{u}^{*}$ and $5{\ensuremath{\sigma}}_{g}^{*}$) with different symmetries resulting from shake-up processes of different origin populated in comparable proportions. The variation of the excitation cross section of these two resonances with photon energy is reported, using two different experimental approaches, which sheds light on the excitation mechanisms. Furthermore, double-core-hole spectroscopy is shown to be able to integrate and even expand information provided by conventional single-core-hole X-ray Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) techniques, revealing, for instance, $g\ensuremath{-}g$ dipole forbidden transitions which are only excited in NEXAFS spectra through vibronic coupling.

Creation of deep core holes with very short (τ≤1 fs) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few-femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1s→σ^{*} excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon.

We have measured resonant-Auger decay following Cl 1s(-1) excitations in HCl and CH3Cl molecules, and extracted the pseudo-cross sections of different Cl 2p(-2) final states. These cross sections show clear evidence of shake processes as well as contributions of electronic state-lifetime interference (ELI). To describe the spectra we developed a fit approach that takes into account ELI contributions and ultrafast nuclear dynamics in dissociative core-excited states. Using this approach we utilized the ELI contributions to obtain the intensity ratios of the overlapping states Cl 1s(-1)4pπ/1s(-1)4pσ in HCl and Cl 1s(-1)4pe/1s(-1)4pa1 in CH3Cl. The experimental value for HCl is compared with theoretical results showing satisfactory agreement.

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.

Shake processes of different origin are identified in the $\mathit{KLL}$ Auger spectrum of ${\mathrm{H}}_{2}\mathrm{S}$ with unprecedented detail. The $\mathit{KLL}$ Auger spectrum is presented together with the S $1{s}^{\ensuremath{-}1}$ photoelectron spectrum including the S $1{s}^{\ensuremath{-}1}{V}^{\ensuremath{-}1}n\ensuremath{\lambda}$ and S $1{s}^{\ensuremath{-}1}2{p}^{\ensuremath{-}1}n\ensuremath{\lambda}$ shake-up satellites with ${V}^{\ensuremath{-}1}$ and $n\ensuremath{\lambda}$ indicating a hole in the valence shell and an unoccupied molecular orbital, respectively. By using different photon energies between 2476 and 4150 eV to record the $\mathit{KLL}$ Auger spectra two different shake-up processes responsible for the satellite lines are identified. The first process is a shake-up during the Auger decay of the S $1{s}^{\ensuremath{-}1}$ core hole and can be described by S $1{s}^{\ensuremath{-}1}\ensuremath{\rightarrow}2{p}^{\ensuremath{-}2}{V}^{\ensuremath{-}1}n\ensuremath{\lambda}$. The second process is the Auger decay of the shake-up satellite in the ionization process leading to S $1{s}^{\ensuremath{-}1}{V}^{\ensuremath{-}1}n\ensuremath{\lambda}\ensuremath{\rightarrow}2{p}^{\ensuremath{-}2}{V}^{\ensuremath{-}1}n\ensuremath{\lambda}$ transitions. By combining the results of photoelectron and Auger spectra the involved ${V}^{\ensuremath{-}1}n\ensuremath{\lambda}$ levels are assigned.

We have observed ${L}_{23}^{2}\ensuremath{-}{M}^{3}$ Auger decay in argon where a double vacancy is filled by two valence electrons and a single electron is ejected from the atom. A well-resolved spectrum of these two-to-one electron transitions is compared to the result of the second-order perturbation theory and its decay branching ratio is determined.

Spectra reflecting the formation of single-site double-core-hole pre-edge states involving the N 1s and C 1s core levels of acetonitrile have been recorded by means of high-resolution single-channel photoelectron spectroscopy using hard X-ray excitation. The data are interpreted with the aid of ab initio quantum chemical calculations, which take into account the direct or conjugate nature of this type of electronic states. Furthermore, the photoelectron spectra of N 1s and C 1s singly core-ionized states have been measured. From these spectra, the chemical shift between the two C 1s−1 states is estimated. Finally, by utilizing C 1s single and double core-ionization potentials, initial and final state effects for the two inequivalent carbon atoms have been investigated.

Resonant X-ray Raman scattering is a powerful tool to study molecular dynamics and subtle chemical effects like the molecular field beyond vibrational and lifetime limitations. Using this technique in the tender X-ray region, gas phase HCl is studied as a benchmark molecule for other compounds like freons, which play an important role in physical-chemical properties of the ozone layer of atmosphere.

A new setup has been designed and built to study organometallic complexes in gas phase at the third-generation Synchrotron radiation sources. This setup consists of a new homemade computer-controlled gas cell that allows us to sublimate solid samples by accurately controlling the temperature. This cell has been developed to be a part of the high-resolution X-ray emission spectrometer permanently installed at the GALAXIES beamline of the French National Synchrotron Facility SOLEIL. To illustrate the capabilities of the setup, the cell has been successfully used to record high-resolution Kα emission spectra of gas-phase ferrocene Fe(C5H5)2 and to characterize their dependence with the excitation energy. This will allow to extend resonant X-ray emission to different organometallic molecules.

Going from a diatomic to a polyatomic linear or non-linear molecule, the description of molecular frame photoemission in photoionization of molecules involves a function of increasing complexity. Using the electron-ion Vector Correlation method, which provides the emission velocity vectors of the emitted charged particles in a dissociative photoionization reaction, generally gives access to Recoil Frame Photoelectron Angular Distributions (RFPADs). We report results for site selected inner-shell photoionization of the N2O molecule induced by elliptically polarized light, where the primary ionization reaction leads to the production of several fragmentation channels. Ion fragment kinetic energy release distributions as well as RFPADs are reported for selected two ion-channels containing the complete parent molecule. Experimental results are compared with recent multi-channel Schwinger configuration interaction (MCSCI) ab initio calculations at the level of the RFPADs. The link with the original computed molecular frame photoelectron angular distributions (MFPADs) is discussed.