<p>This thesis addresses the electronic structure of molecular and correlated solids using resonant inelastic soft X-ray scattering (RIXS), non-resonant X-ray emission, photoemissionand X-ray absorption spectroscopies. The use of monochromatised synchrotron radiation and improved energy resolution for X-ray emission have made it possible to elucidate the normal state transport properties and to get further insight into the electron-vibration coupling in fullerenes and the related compounds. The latter is particularly important in order to understand the physical mechanism of superconductivity in fullerene materials. The characteristic intermolecular charge transfer times in K₃C₆₀ are found to be longer than the X-ray scattering time-scale (a few femtoseconds). The slow intermolecular charge transport emphasizes that the reduced fullerene compounds can not be treated as simple metals, but rather as systems with strong electron correlation. The electron structure and the bonding character of the more covalent transition metal (V, Ti, Nb) fullerides have been addressed. Evidence indicating the existence of chemical bond between the metal atom(s) and C₆₀ is presented, and the nature of the bond is discussed by comparing RIXS spectroscopic measurements and theoretical predictions. The (crystal) momentum conservation is discussed by comparing the spectroscopic data of a quasi-1D (carbon nanotubes) and quasi-2D (graphite) systems. Finally, the intra-atomic electron-electron correlation is discussed in the case of double core-hole state photo-excitation and de-excitation processes. RIXS including intermediate states with two core vacancies has been observed for the first time in the soft X-ray region.</p>

<p>Ion insertion into electrode materials can be used to store energy in battery applications. In this thesis, photoelectron spectroscopic and x-ray absorption spectroscopic methods have been used to study the change of the electronic structure of host materials during electrochemical ion insertion. </p><p>Specifically, the properties of ion insertion into nanoporous TiO₂ were studied. It is demonstrated that the insertion of Li ions results in a reduction of the Ti⁴⁺ sites in TiO2 to Ti³⁺ sites close to the inserted Li ion. The intensity of the Ti³⁺ is directly correlated to the number of inserted electrons. It is also shown that the two phases resulting from moderate insertion can be detected by studying the electronic structure of inserted Li ions and the behavior observed can be correlated with electrochemical measurements. </p><p>Insertion of ions into tungsten oxides is a potential candidate for smart window and display applications. Ion insertion into these materials was, also studied with electron spectroscopic methods. The insertion of H⁺ reduces W⁶⁺ to W⁵⁺ and further insertion results in a reduction to W⁴⁺. Cyclic voltammerty shows two reduction peaks where the first peak implies reduction of W⁶⁺ to W⁵⁺ and the second peak can be associated with further reduction to W^4+.</p><p>During the first charge/discharge cycles of a battery based on graphite anodes a solid electrolyte interface layer is formed on the electrode surface. This layer consumes some of the charge carrying Li ions, hence decreases the capacity of the battery. A careful characterization of this layer has been performed to aid in the further development of this type of battery.</p>

<p>A number of nanostructured systems has been investigated by means of Photoemission and X-ray absorption spectroscopies and by Scanning tunneling microscopy with emphasis on the geometric and electronic structure and the excited-state charge transfer dynamics. These systems comprise aromatic molecules on semiconductor surfaces (titanium dioxide), metal clusters, and an alkali-C₆₀ compound. </p><p>Electronic and geometric structure are complementary to each other, and changes in the geometric structure are accompanied by changes in the electronic structure. Therefore, a detailed investigation of the latter makes it possible to draw conclusions on the former. In particular, this close relationship has been used to characterise the adsorbate geometry of the pyridine-carboxylic acid monomers on rutile TiO₂(110), which is determined by the strong substrate bond as well as interadsorbate interactions. Similarly, it has been found that bi-isonicotinic acid adsorbs on a nanostructured anatase TiO₂ film by forming strong bonds between both carboxylic groups and the substrate titanium atoms. For deposited metal clusters, the core binding energies are found to mirror the cluster size.</p><p>Resonant core electron spectroscopies have been employed to elucidate the excited-state charge transfer dynamics with respect to the transfer of an excited electron from the bi-isonicotinic acid and isonicotinic acid adsorbates to a titanium dioxide semiconductor surface. An important aspect has been the development of new variations of the method in order to be able to unravel the spectra of these relatively complex systems. While a strong excitonic effect localises the excited electron on the adsorbate for the lowest excited state, excitation to the higher excited states leads to an ultrarapid charge transfer on a low- to sub-femtosecond timescale.</p><p>In LiC₆₀ the character of the alkali-C₆₀ bond has been investigated. The balance between the different energy contributions points to an ionic bond with an important element of covalency. </p>

<p>Quantum Chromodynamics (QCD) is the theory of the strong interaction, one of the fundamental forces of nature. The interactions between quarks are mediated by gluons, which are the colour-charged gauge fields in QCD. Hard processes with a large momentum transfer can be calculated using perturbation theory, while soft processes with a small momentum transfer are poorly understood. In this thesis, various aspects of the gluon interactions are studied based on the interplay between hard and soft processes.</p><p><i>Soft gluon exchanges</i> do not affect the dynamics of a hard process, but can rearrange the colour topology, resulting in different final states. The soft colour interaction models employ this idea and give a good description of all diffractive hard scattering data observed in <i>p</i><i>p</i> collisions (<i>W</i>, <i>Z</i>, dijets, <i>b</i><i>b</i>, <i>J</i>/ψ). This thesis also presents predictions for diffractive Higgs and γγ production at present and future hadron colliders.</p><p><i>Multiple gluon exchanges</i> give rise to saturation effects in hadronic collisions at high energies. Implementing this idea in photon-photon collisions gives new insight into the quantum structure of the photon and its interactions at high energies. When combined with perturbative calculations for single gluon exchange, the obtained results are in good agreement with experimental data from e⁺e^- colliders.</p><p><i>Off-shell gluon distributions</i> in the photon give another perspective on the photon structure and have been parameterized for the first time in this thesis. These are useful for calculating cross sections of processes where the effects of transverse momenta are crucial, for example heavy quark production in γ<i>p</i> or γγ collisions.</p><p><i>Quantization of gauge fields</i> which have a richer gauge structure than the gluons in QCD, is studied using the powerful BRST quantization formalism. Thus, first-stage reducible theories, like topological Yang-Mills and spin-5/2 gauge fields, are successfully quantized in an irreducible way.</p><p>Understanding gluon interactions and the interplay between soft and hard processes paves the way towards solving the longstanding problem of <i>confinement</i> in QCD.</p>

<p>The physical and chemical properties of matter are to a high degree determined by the electronic structure. One of the most powerful experimental techniques to study the electronic structure is electron spectroscopy. Conventionally most of the investigations on molecules, carried out using this technique, have dealt with static information such as binding energies and localization of the electron. This thesis focuses on the currently expanding field more concerned with dynamic effects such as lifetimes and dissociation times. In particular, resonantly excited molecules have been studied. </p><p>As an example, we have used the "core hole clock" method to determine the dissociation times of core excited water and ammonia molecules. These experiments are possible using a synchrotron light source and the experiments are based on ultra-fast dissociation of resonantly excited states. A similar experiment on doubly core-excited nitrogen molecules have revealed no sign of ultra-fast dissociation as the resulting spectral features contain vibrational progressions and therefore result from molecular decay.</p><p>Molecules that dissociate on an ultra-fast timescale, i.e. in the low femtosecond regime, are interesting for several reasons. For instance, decay occurring in core excited oxygen fragments can be used to demonstrate a localization of the core hole through the existence of a Doppler effect. Also, the nature of the molecular intermediate state leading to ultra-fast dissociation can be of interest. For the oxygen molecule there is a debate concerning the assignment of the large absorption structure near the O1s ionization energy. We are able to disclose which photon wavelengths lead to ultra-fast dissociation.</p><p>Direct information on the time dependence of electronic structure and molecular dynamics during the ionization process can be obtained through the use of fast pulsed lasers in pump-probe experiments. For such studies we have used the terawatt laser at the Lund Laser Center providing pulses down to 110 fs long to observe the decay of two different states in valence excited acetylene.</p>

<p>Resonant electron spectroscopy has been performed on the diatomic molecules CO, N₂ and HCl. Core-excitations were made to bound and dissociative intermediate electronic states. Fundamental interference phenomena are observed and discussed in the framework of ”X-ray Raman Scattering Theory”. For C1<i>s→π</i>* core-excited CO higher vibrational levels, which are difficult to discerne in a total yield photoabsorption spectrum, are revealed. For N1s→π* core-excited N₂ the interaction of the B²Σ⁺_u final state with the neighbouring C²Σ⁺_ustate leads to breakdown of the commonly used ”participator” and ”spectator” classification. For negative photon frequency detuning with respect to the same resonance, an interference quenching of a certain vibrational line in the X²Σ⁺_g final state of N⁺₂ has been observed and analysed, showing a novel way to determine the equilibrium bond distance of the core-excited state. The duration time concept for the scattering process is refined in terms of partial and mean duration time, explaining detuning asymmetries for the X²Σ⁺_g, A²Π_uand B²Σ⁺_u final states of N⁺₂ . The role of monochromator stray-light on the formation of electron spectra has been investigated in the vincinity of the N1s→π* resonance of N₂, a method to drastically reduce undesired ”Stokes spectral features” is demonstrated. The decay of a triply-excited intermediate state in N₂, located above the N1s ionisation threshold, has been studied, revealing a ”double spectator” type mechanism. In HCl the decay to the 4σ^-1 inner valence region upon excitation to the ultrafast dissociative <i>Cl</i>2<i>p</i>^-16σ* intermediate state exhibits a novel type of interference involving ”atomic” and ”molecular” decay channels, giving rise to a ”continuum-continuum interference hole” in the electron spectrum. A selective population of spin-orbit split final state vibrational components has been observed in the decay to the X²Π final state in HCl⁺ upon photon energy tuning to either of the spin-orbit split components of the <i>Cl</i>2<i>p</i>^-16σ* core-excited state. </p><p>Direct photoelectron spectroscopy on free, neutral Ar, Kr and Xe clusters has been performed and changes in the electronic structure upon cluster formation has been investigated. Band structure formation for some of the inner valence levels is encountered, making a description of these orbitals in the sense of localised or delocalised difficult. The first resonant Auger electron spectra of free rare gas clusters are presented and discussed. A ”spectroscopic-loop” method to decompose complex cluster photoabsorption spectra is experimentally demonstrated.</p>

<p>Quantum chromodynamics (QCD) is the fundamental theory in elementary particle physics that describes the strong interaction in terms of exchanges of force-carrying, <i>colour</i>-charged particles known as gluons. Although well-established through experimental verifications, there are fundamental unsolved problems in the theory.</p><p>In this thesis, some novel aspects of strong interaction dynamics are studied in the context of <i>colour singlet exchange</i> processes — interactions where complex systems of gluons with no net colour charge are exchanged. Both perturbative and non-perturbative QCD methods are used, as well as Monte Carlo computer simulations.</p><p><i>Soft colour interactions</i> in the final state of a high energy collision can lead to effective colour singlet exchange. Non-perturbative models for such interactions are shown to give a good description of diffractive production of <i>W</i>, <i>Z</i>, <i>b</i><i>b</i>, <i>J</i>/<i>ψ</i> and jets in <i>p</i><i>p</i> collisions at the Tevatron. Predictions are given for diffractive Higgs boson and prompt photon production at hadron colliders.</p><p><i>Rapidity gaps between jets</i> is a new phenomenon which is studied with an improved perturbative calculation of hard colour singlet exchange using the BFKL equation, taking into account previously neglected contributions and non-leading logarithmic corrections. Including also underlying soft rescattering effects, the complete model reproduces well data from the Tevatron.</p><p><i>Diffractive vector meson production</i> through hard colour singlet exchange in <i>γp</i> collisions is studied in the framework of the conformal invariant non-forward solution of the BFKL equation. Expressions for helicity-dependent amplitudes are derived, and the results show good agreement with data on <i>J</i>/<i>ψ</i> and <i>ρ</i> production from the <i>ep</i> collider HERA.</p><p>These studies lead to a deeper knowledge of complex gluon dynamics, and therefore advance our understanding of QCD.</p> / <p>X</p>

<p>The electronic structure of the ozone molecule O₃ has been studied with spectroscopy techniques and computations. The investigation was focused on O₃ in a core-hole state. The electronic configuration and the nuclear dynamics have been found to be highly correlated.</p><p>This electron correlation is mapped out for the two chemically different sites in the molecule: the central and the terminal oxygen. The energy difference between the corresponding core orbitals is 4.58 eV, which allows for site-selective core ionization and core excitation. </p><p>The influence of the core-hole site on the electronic structure is substantial, which is shown with ion and electron spectroscopy data and ab-initio quantum chemical computations. Moreover, the induced nuclear motion differs considerably for the two core-hole sites.</p><p>One of the core-excited states is proven to be ultra-fast dissociative. An analysis of the data with a formalism for two-body dissociation disclosed the localized character of core excitation. The symmetry-equivalent terminal-oxygen core orbitals do have very little overlap, so that a delocalized model for the core excitation becomes inadequate.</p><p>Moreover, core-excitation opens up a decay channel to a valence-ionized state that has not been observed with photoionization. The reason for this state to have low cross section for photoionization is illuminated with a CASSCF computation of the electronic configuration. The configuration of the state was found to be very distinct from the ground state configuration.</p><p>Another effect of configuration-interaction was found in MRCI computations of the core- ionized states. Several local minima with distinct electronic configurations could be identified.</p>

Quantum chromodynamics (QCD) is the fundamental theory in elementary particle physics that describes the strong interaction in terms of exchanges of force-carrying, colour-charged particles known as gluons. Although well-established through experimental verifications, there are fundamental unsolved problems in the theory. In this thesis, some novel aspects of strong interaction dynamics are studied in the context of colour singlet exchange processes — interactions where complex systems of gluons with no net colour charge are exchanged. Both perturbative and non-perturbative QCD methods are used, as well as Monte Carlo computer simulations. Soft colour interactions in the final state of a high energy collision can lead to effective colour singlet exchange. Non-perturbative models for such interactions are shown to give a good description of diffractive production of W, Z, bb, J/ψ and jets in pp collisions at the Tevatron. Predictions are given for diffractive Higgs boson and prompt photon production at hadron colliders. Rapidity gaps between jets is a new phenomenon which is studied with an improved perturbative calculation of hard colour singlet exchange using the BFKL equation, taking into account previously neglected contributions and non-leading logarithmic corrections. Including also underlying soft rescattering effects, the complete model reproduces well data from the Tevatron. Diffractive vector meson production through hard colour singlet exchange in γp collisions is studied in the framework of the conformal invariant non-forward solution of the BFKL equation. Expressions for helicity-dependent amplitudes are derived, and the results show good agreement with data on J/ψ and ρ production from the ep collider HERA. These studies lead to a deeper knowledge of complex gluon dynamics, and therefore advance our understanding of QCD. / X

Partitioning and transmutation of plutonium, americium, and curium is inevitable if the radiotoxic inventory of spent nuclear fuel is to be reduced by more than a factor of 100. But, admixing minor actinides into the fuel severely degrades system safety parameters, particularly coolant void reactivity, Doppler effect, and (effective) delayed neutron fractions. The incineration process is therefore envisioned to be carried out in dedicated, accelerator-driven sub-critical reactors (ADS). However, ADS cores operating in concert with light-water reactors (two-component scenario) also exhibit high burnup reactivity swing with penalty on the system performance/economy. In the frame of this design work, we attempted, by choice of coolant and optimisation of fuel concept and core design, to achieve favourable neutronic, burnup and safety characteristics of the transuranium ADS burner. Key thermal hydraulic and material-related constraints were respected. A novel fuel matrix material, hafnium nitride, was identified as an attractive diluent option for highly reactive transuranics. (TRU,Hf)N fuels appeared to have a good combination of neutronic, burnup and thermal characteristics: maintaining hard neutron spectra, yielding acceptable values of coolant void reactivity and source efficiency, and providing small burnup reactivity loss. A conceptual design of a (TRU,Hf)N fuelled, lead/bismuth eutectic cooled ADS was developed. The average discharge burnup of 20% fissions per initial metal atom could be reached even without fuel reshuffling. The fission fraction ratios of even-neutron number americium nuclides are increased by a factor of two in comparison to burners with inert matrix based fuels. Hence, thanks to the reduced production of higher actinides and helium, fuel cycle economy is improved. The coolant void worth proved to be a strong function of the fuel composition - reactor cores with high content of fertile material or minor actinides in fuel exhibit larger void reactivities than systems with plutonium-rich, inert matrix fuels. In reactor systems cooled by lead/bismuth eutectic, a radial steel pin reflector significantly lowered coolant void reactivity. For transuranic fuel, fertile and strongly absorbing matrices exhibited increasing void worth with increasing pitch, while the opposite was valid for the coolant void worth of inert matrix fuels. Large pitches also appeared to be beneficial for limiting the reactivity worth of the cladding material and improving source efficiency. The economy of the source neutrons was investigated as a function of core and target design. An incentive to design the core with as low target radius as allowable by the thermal constraints posed by the ability to dissipate accelerator beam power was identified.