The main focus of this thesis is ab initio modeling of core level spectra with a high-level quantum chemical description both of the chemical interactions and of local atomic multiplet effects. In particular, the combination of calculations and synchrotron-based core-level spectroscopy aims at understanding the local structure of the electronic valence in transition metal complexes, and the details of the solvation mechanisms of electrolyte solutions, systems relevant for the dye-sensitized solar cell. Configurational sampling in solution is included through molecular dynamics simulations.

Transition metal complexes are studied with x-ray absorption (XA) and resonant inelastic scattering (RIXS) spectroscopy, characterizing excited states with atomic site specificity. The theoretical multiconfigurational method, applying an active-space partitioning of the molecular orbitals (RASSCF), is used to assign the transitions observed in spectra of hydrated Ni²⁺ explicitly, including charge transfer and multiplet effects.

Furthermore, the solvent-induced binding energy properties of the I^- and I₃^- anions in aqueous, ethanol, and acetonitrile solutions are analyzed using photoelectron spectroscopy (XPS). The study shows that specific ion–solvent interactions are important for the core-level binding energy shifts in solution. The special case with I₃^- dissolved in water, where hydrogen bonding causes breaking of the molecular symmetry, is treated and proves that the geometry changes influence the photoelectron spectrum of aqueous I₃^- directly.

This thesis is based on theoretical studies of the molecular and electronic structure of solvated ions and molecules. Very detailed information of the system can be obtained from theoretical calculations, but a realistic model is dependent on an accurate computational method. Accurate calculations of core level electronic spectra, and evaluation of the modeling against experiments, are central parts of this work. The main tools used for characterization of the systems are high-level quantum chemistry and molecular dynamics simulations. 

Molecular components in solutions are involved in many key processes converting sunlight into chemical or electrical energy. Transition metal complexes, with their pronounced absorption in the visible light region of the electromagnetic spectrum, are core components in various energy conversion applications, and the iodide/triiodide redox couple is a commonly used electrolyte. The local structure of the electronic valence in transition metal complexes and the details of the solvation mechanisms of electrolyte solutions are investigated through the combination of computational modeling and core level spectroscopy. The studies of model systems show that interactions between the solute and solvent are important for the electronic structure, and knowledge of the details in model systems studied can be relevant for energy conversion applications. Furthermore, high-level quantum chemistry has been applied for interpreting time-resolved spectra, where the electronic structure of a metal complex is followed during a photoinduced chemical reaction in solution.

With advanced modeling in combination with recent experimental developments, more complex problems than previously addressed can be dissected.