In recent years double core-hole states are intensively studied since their chemical shifts provide detailed information about initial-state and relaxation effects in a molecule. We derived the Si 1s−1, 2s−1, and 2p−1 binding energies as well as the Si 2s−2, 2s−1, 2p−1, and 2p−2 double-core hole binding energies of different SiX4 systems in order to derive the chemical shifts. Based on these results we created Wagner plots, which give insight in the initial state and the relaxation effects in the different molecules.

We present the first-ever measurement of nondipole chiral angular distribution parameters for C 1s photoemission from each enantiomer of camphor in the photon energy range 296-343eV using linearly polarized light. The angular distribution parameters are determined to be enantiomer-specific, suggesting a new form of linear dichroism.

Electronic core levels in molecules are highly localized around one atomic site. However, in single-photon ionization of symmetric molecules, the question of core-hole localization versus delocalization over two equivalent atoms has long been debated as the answer lies at the heart of quantum mechanics. Here, using a joint experimental and theoretical study of core-ionized carbon disulfide (CS2), we demonstrate that it is possible to experimentally select distinct molecular-fragmentation pathways in which the core hole can be considered as either localized on one sulfur atom or delocalized between two indistinguishable sulfur atoms. This feat is accomplished by measuring photoelectron angular distributions within the frame of the molecule, directly probing entanglement or disentanglement of quantum pathways as a function of how the molecule dissociates.

Relative partial cross sections have been measured following photoexcitation of atomic chlorine near the Cl 2p and Cl 1s ionization thresholds. In addition, Breit-Pauli R-matrix calculations have been carried out in the region of the 2p thresholds, and the results are compared with experiment. Owing to angular-momentum considerations, it was found that the resonances associated with the higher 2p(-1) thresholds should be significantly wider than the lower ones, and this is borne out in both the experimental and the theoretical results. It is shown that a large number of resonance series contribute to the cross section, which make it difficult to untangle, and suggestions for further work to better understand the spectra are presented.

We present a combined experimental and theoretical study of isolated CH(3)Cl molecules using resonant inelastic x-ray scattering (RIXS). The high-resolution spectra allow extraction of information about nuclear dynamics in the core-excited molecule. Polarization-resolved RIXS spectra exhibit linear dichroism in the spin-orbit intensities, a result interpreted as due to chemical environment and singlet-triplet exchange in the molecular core levels. From analysis of the polarization-resolved data, Cl 2p(x, y) and 2p(z) electronic populations can be determined.

Electronegativity is a well-known property of atoms and substituent groups. Because there is no direct way to measure it, establishing a useful scale for electronegativity often entails correlating it to another chemical parameter; a wide variety of methods have been proposed over the past 80 years to do just that. This work reports a new approach that connects electronegativity to a spectroscopic parameter derived from resonant inelastic x-ray scattering. The new method is demonstrated using a series of chlorine-containing compounds, focusing on the Cl 2p(-1)LUMO(1) electronic states reached after Cl 1s → LUMO core excitation and subsequent KL radiative decay. Based on an electron-density analysis of the LUMOs, the relative weights of the Cl 2p(z) atomic orbital contributing to the Cl 2p(3/2) molecular spin-orbit components are shown to yield a linear electronegativity scale consistent with previous approaches.

We present a series of photoabsorption and partial-ion-yield experiments on thionyl chloride, SOCl(2), at both the sulfur and chlorine K edges. The photoabsorption results exhibit better resolution than previously published data, leading to alternate spectral assignments for some of the features, particularly in the Rydberg-series region. Based on measured fragmentation patterns, we suggest the LUMO, of a(') character, is delocalized over the entire molecular skeleton. Unusual behavior of the S(2 +) fragment hints at a relatively localized bond rupture (the S-O bond below the S K edge and the S-Cl bonds below the Cl K edge) following excitation to some of the higher lying intermediate states.

We experimentally observed interference effects in elastic x-ray scattering from gas-phase HCl in the vicinity of the Cl K edge. Comparison to theory identifies these effects as interference effects between non-resonant elastic Thomson scattering and resonant Raman scattering. The results indicate the non-resonant Thomson and resonant Raman contributions are of comparable strength. The measurements also exhibit strong polarization dependence, allowing an easy identification of the resonant and non-resonant contributions.

Photoionization cross-section measurements for atomic nitrogen in the region of the K-edge have been made at the Advanced Light Source for the first time and are suitably reproduced by R-matrix calculations.

We report an extensive study on partial-ion-yield spectroscopy around the Cl 1s and 2p ionization thresholds for Cl-2. All positive ion channels, several with the same mass/charge ratio, which could be distinguished by taking the advantage of the Cl-37 isotope, have been measured at a photon resolution of nearly 6500. At the Cl 1s ionization threshold, no significant differences are reported between the absorption and the partial-ion yields. In contrast, near the 2p ionization thresholds, we detect large variations in the fragmentation patterns following excitations to the Rydberg series when comparing the atomic fragment ions to the molecular fragment ions. We attribute the different behaviours to the more-or-less diffuse nature of Rydberg states with different angular momenta.

Partial ion yield spectroscopy was used to study fragmentation processes in cyanogen after C and N photoexcitation. The interpretation of the core excitation spectrum mostly follows the literature, but the high resolution has in some cases allowed a more detailed assignment. Using the fact that in Rydberg states there is an intensity increase as the fragmentation process becomes more extensive compared to valence orbitals, we have been able to distinguish resonances with valence and Rydberg character. Furthermore, we have been able to assign features in the ionization continuum as arising from double excitations or shape resonances, by observation of the suppression of anion yield at shape resonances.

We present a partial ion yield experiment on freon 13, CF(3)Cl, excited in the vicinity of the C 1s and Cl 2p ionization thresholds. We have collected a large amount of cationic fragments and a few anionic fragments at both edges. We have observed a strong intensity dependence of Rydberg transitions with ion fragment size for the CF(n)Cl(+) and CF(n)(+)/F(+) (n=0-3) series at both the Cl 2p and C 1s ionization edges. Selectivity in the fragmentation processes involving the C-Cl and C-F bonds are highlighted by the intensities of the C 1s to lowest unoccupied molecular orbital (LUMO) and LUMO+1 transitions measured on the CF(n)Cl(+) and CF(n)(+) yields. Equally, by comparison with their cation counterpart, we discuss possible bond-length dependence for the anion formation at the carbon 1s edge.

We investigated the photofragmentation properties of two three-membered ring heterocyclic molecules, C2H4O and C2H4S, by total and partial ion yield spectroscopy. Positive and negative ions have been collected as a function of photon energy around the C 1s and O 1s ionization thresholds in C2H4O, and around the S 2p and C 1s thresholds in C2H4S. We underline similarities and differences between these two analogous systems. We present a new assignment of the spectral features around the C K-edge and the sulfur L2,3 edges in C2H4S. In both systems, we observe high fragmentation efficiency leading to positive and negative ions when exciting these molecules at resonances involving core-to-Rydberg transitions. The system, with one electron in an orbital far from the ionic core, relaxes preferentially by spectator Auger decay, and the resulting singly charged ion with two valence holes and one electron in an outer diffuse orbital can remain in excited states more susceptible to dissociation. A state-selective fragmentation pattern is analyzed in C2H4S which leads to direct production of S2+ following the decay of virtual-orbital excitations to final states above the double-ionization threshold.

Polarization-dependent resonant inelastic x-ray scattering (RIXS) is shown to be a new probe of molecular-field effects on molecular electronic structure. Combining experiment and theory, linear dichroism in Cl 2p RIXS following Cl 1s excitation in HCl, Cl2, and CF3Cl is ascribed to molecular-field effects, indicating polarized-RIXS provides a direct probe of spin-orbit-state populations generally applicable to all molecules.

We present a combined theoretical and experimental study of molecular field effects on molecular core levels. Polarization-dependent resonant inelastic x-ray scattering is observed experimentally after resonant $K$-shell excitation of ${\text{CF}}_{3}\text{Cl}$ and HCl. We explain the linear dichroism observed in spin-orbit level intensities as due to molecular field effects, including singlet-triplet exchange, and interpret this behavior in terms of population differences in the $2{p}_{x,y,z}$ inner-shell orbitals. We investigate theoretically the different factors that can affect the electronic populations and the dynamical $R$ dependence of the spin-orbit ratio. Finally, the results obtained are used to interpret the $L$-shell absorption spectra of the two molecules.

Calculations and measurements of the Xe 5s and 5p nondipole photoelectron asymmetry parameters are obtained, which present clear evidence of the existence of quadrupole Cooper minima, i.e., minima in quadrupole matrix elements as a function of energy, in the photoionization process. This verifies earlier predictions of quadrupole Cooper minima.

We report a study using partial-ion-yield spectroscopy around the Cl 2p ionization threshold of HCl. All cation channels have been measured, while no evidence for anion production was obtained. The absence of any detectable H− can be related to the electronegativity difference between the two atoms and the observed low probability of directly creating Cl++ and Cl+++. In the photon-energy region around the Cl 2p3/2,1/2 → 6σ* excitation process, production of H+ is almost completely suppressed, which indicates a dominant ultrafast dissociation process leading to neutral H.

Polarization-dependent resonant inelastic x-ray scattering (RIXS) is shown to be a new probe of molecular-field effects on the electronic structure of isolated molecules. A combined experimental and theoretical analysis explains the linear dichroism observed in Cl 2p RIXS following Cl 1s excitation in HCl and CF3Cl as due to molecular-field effects, including singlet-triplet exchange, indicating polarized-RIXS provides a direct probe of spin-orbit-state populations applicable to any molecule.