We integrate full core-hole density-functional theory with Franck-Condon calculations, considering Duschinsky rotation, to simulate vibrationally resolved C 1s x-ray photoelectron spectra of eight linear alkanes, from methane to octane (CnH2n+2, n=1-8). Results align excellently with experimental absolute binding energies and profiles. The spectrum of ethane serves as a "spectral seed,"with each longer alkane's atom-specific spectrum displaying similar characteristics, albeit with shifts and slight intensity adjustments. Detailed assignments clarify the distinct spectra in short alkanes (n=1-4) and their stabilization in long alkanes (n=5-8). Carbons are classified as central or distal (C1 and C2), with central carbons contributing nearly identically to the lowest-energy feature A, while distal carbons contribute to the second-lowest-energy feature B (both are 0-0 transitions). Increasing molecule size adds more central carbons, enhancing feature A and weakening feature B. Our analysis identifies two dominant Franck-Condon active vibrations: a localized C∗-H stretching (approximately 3400-3500 cm-1) and a delocalized C-H bending (approximately 1400-1500 cm-1) modes. Structural analysis shows that core ionization minimally affects alkane geometry, less than in ring compounds from previous studies. This work extends our protocol from rigid ring compounds to flexible molecules, contributing to building a high-resolution theoretical x-ray photoelectron spectroscopy library and enhancing the understanding of vibronic coupling.

With the development of new generation synchrotron facilities, the performances of various X-ray spectroscopies have become more advanced. In order to interpret the X-ray spectrum experiments of various novel materials related to transition metal and rare earth elements, new advanced theoretical methods are required. The present thesis incorporates four modus operandi based on the classic multiplet theory to study the core level X-ray spectroscopy of transition metal and rare earth element. The four approaches consist of new methods developed from classic multiplet approach to high level first-principles method assisted multiplet calculation. Some methods are selected from previous researches and some are invented by original researches. These methods are integrated together to form a complete set of multiplet computational methods. This set of multiplet computational methods can perform calculations on various X-ray spectroscopies such as XAS, XPS, XES and RIXS related to the core-level electron. These wide range of spectroscopic methods coupled to different multiplet theory approaches serve as efficient tools to understand the electronic structure of metal sites and their unique contribution to the physical/chemical properties of the materials.

The thesis creatively improves the classic multiplet theory on several aspects: (1) the relation between crystal field parameters and local structure factors; (2) the difficulty of processing point group symmetry branching chain in low symmetric structure; (3) the first-principles calculation of semi-empirical parameters. Four modus operandi are presented in this thesis: the first is the classic multiplet theory consisting of the multiplet effect, crystal field effect and charge transfer effect via several semi-empirical parameters as description for these effects. The second level multiplet theoretical approach analyze the crystal field potential matrix in various symmetries according to the point group symmetry branching rules. Then the crystal field effect parameters used in classic multiplet theory are linked analytically to the specific structural factors such as bond length and angles. This approach is a good tool to study the structural distortion from higher to lower order symmetry with analysis of X-ray spectral feature changes in experiment. The third modus operandi adopts large cluster model consisting of point charges at equivalent atoms position to simulate the crystal field effect on the center metal site. This approach handles low order symmetric crystal field with long range effect in multiplet calculation in an easier way than the classic multiplet theory. The fourth modus operandi initially studies the system of interest in first-principles calculation for the electronic wavefunctions. Then the electronic wavefunctions are used to derive the maximally localized Wannier functions at metal/ligand sites. The analysis of these Wannier functions provide a lot of semi-empirical parameters required in the classic multiplet calculation approach in a first-principles way. This modus operandi has substantially resolved the problem of finding the best set of semi-empirical parameters to fit the calculated X-ray spectrum with experimental data.

In order to study the core electrons of the light elements (such as C/N/O) around center metal ions, a theoretical calculation method used to study the core electrons' vibrationally-resolved X-ray spectroscopy is also introduced as a complementary research and applied to C1s core ionized XPS calculation as an example.

Med utvecklingen av nya generationens synkrotronanläggningar har prestandan för olika röntgenspektroskopier blivit mer avancerad. För att tolka röntgenspektrumexperiment av olika nya material relaterade till övergångsmetaller och sällsynta jordartsmetaller krävs nya avancerade teoretiska metoder. Denna avhandling inkorporerar fyra metoder baserade på den klassiska multiplettläran för att studera röntgenspektroskopi på kärnenerginivån för övergångsmetaller och sällsynta jordartsmetaller. De fyra metoderna består av nya metoder som utvecklats från den klassiska multiplettläran till multiplettberäkning med hjälp av högnivå-först-principer-metoder. Vissa metoder har valts från tidigare forskning och några har uppfunnits genom originalforskning. Dessa metoder integreras för att bilda en komplett uppsättning av multiplettberäkningsmetoder. Denna uppsättning av multiplettberäkningsmetoder kan utföra beräkningar av olika röntgenspektroskopier som XAS, XPS, XES och RIXS relaterade till elektroner på kärnenerginivån. Denna breda spektrum av spektroskopiska metoder som kopplas till olika multipletteteoretiska tillvägagångssätt fungerar som effektiva verktyg för att förstå den elektroniska strukturen hos metalliska platser och deras unika bidrag till materialets fysikaliska/kemiska egenskaper.

Avhandlingen förbättrar på ett kreativt sätt den klassiska multiplettläran på flera områden: (1) förhållandet mellan kristallfältparametrar och lokala strukturfaktorer, (2) svårigheten med att hantera förgreningskedjor i punktgruppsymmetri för strukturer med låg symmetri, (3) först-principer-beräkning av semi-empiriska parametrar. Fyra metoder presenteras i denna avhandling: den första är den klassiska multiplettläran som omfattar multiplett-effekten, kristallfältseffekten och laddningsöverföringseffekten genom flera semi-empiriska parametrar som beskriver dessa effekter. Den andra multiplett-teoretiska tillvägagångssättet analyserar kristallfältspotensialmatrisen i olika symmetrier enligt reglerna för punktgruppsymmetri. Därefter kopplas de kristallfältseffektparametrar som används i den klassiska multiplettläran analytiskt till specifika strukturella faktorer som bindningslängd och vinklar. Detta tillvägagångssätt är ett bra verktyg för att studera strukturell distorsion från högre till lägre ordningssymmetri med analys av förändringar i röntgenspektrala funktionsändringar i experiment. Det tredje tillvägagångssättet använder en stor klustermetod som består av punktladdningar på ekvivalenta atompositioner för att simulera kristallfältsinverkan på metallcentralen. Detta tillvägagångssätt hanterar kristallfält med låg symmetri och lång räckvidd i multiplettberäkningar på ett enklare sätt än den klassiska multiplettläran. Det fjärde tillvägagångssättet studerar initialt det intressanta systemet med först-principer-beräkningar av elektronvågfunktioner. Därefter används dessa elektronvågfunktioner för att härleda maximalt lokaliserade Wannier-funktioner vid metall-/ligandpositioner. Analysen av dessa Wannier-funktioner ger många av de semi-empiriska parametrar som krävs i den klassiska multiplettberäkningsmetoden på ett först-principer-sätt. Detta tillvägagångssätt har i stor utsträckning löst problemet med att hitta den bästa uppsättningen semi-empiriska parametrar för att anpassa de beräknade röntgenspektrumen med experimentella data.

För att studera de lättas elektroner (som C/N/O) runt centrala metalljoner introduceras även en teoretisk beräkningsmetod för att studera röntgenspektrum med vibrationell upplösning för kärnelektroner som ett kompletterande forskningsområde och tillämpas på beräkningar av C1s-kärnenerginivåns XPS som ett exempel.

Vibrationally resolved C 1s X-ray photoelectron spectra (XPS) of a series of six polycyclic aromatic hydrocarbons (PAHs; phenanthrene, coronene, naphthalene, anthracene, tetracene, and pentacene) were computed by combining the full core hole density functional theory and the Franck–Condon simulations with the inclusion of the Duschinsky rotation effect. Simulated spectra of phenanthrene, coronene, and naphthalene agree well with experiments both in core binding energies (BEs) and profiles, which validate the accuracy of our predictions for the rest molecules with no high-resolution experiments. We found that three types of carbons i (inner C), p (peripheral C bonded to three C atoms), and h (peripheral C bonded to an H atom) show decreasing BEs. In linear PAHs (the latter four), h-type carbons further split into h1 or h2 (on inner or edge benzene ring) subtypes with chemical shifts of ca. 0.2–0.4 eV. All major Franck–Condon-active modes are characterized to be in-plane vibrations: low-frequency (<800 cm–1) C–C ring deformation modes play an essential role in determining the peak asymmetries; and for each h-type carbon a high-frequency (ca. 3600 cm–1) C*–H stretching mode is responsible for the high-energy tail. We found that core ionization leads to reduction of all C*–C and C*–H bond lengths and ring deformation with a definite direction. Based on theoretical spectra of four linear PAHs, we found asymptotic relations and anticipated possible spectral features for even larger linear PAHs. Our calculations provide accurate reference spectra for XPS characterizations of PAHs, which are useful in understanding the vibronic coupling effects in this family. 

Vibronic coupling plays a pivotal role in molecular spectroscopy. We present a theoretical study on vibrationally resolved x-ray photoelectron spectra (XPS) of seven azines (CxHyNz; pyridine, three diazines, two triazines, and one tetrazine) at the nitrogen 1s edge, to explore the vibronic coupling effects as influenced by consecutive replacement of the CH group with a N atom. Franck-Condon simulations were performed with the Duschinsky rotation effect included, where the electronic structure was calculated by the density functional theory. Validations on pyrimidine show good agreement with the experiment, weak functional dependence, and weak mode mixing effect. We observed an evident blue shift in binding energies with the increasing number of N atoms in this series, together with molecule-dependent vibronic fine structures. These molecules have either C2v or Cs molecular symmetry at the optimized core-ionized geometries. Franck-Condon-active vibrational modes were identified to be low frequency (500–1650 cm−1), totally symmetric (A1 or A′), in-plane ring deformation modes. Core ionization on N∗ always leads to elongation of the N∗−N bond length, accompanied by an increase of the ∠C−N∗−X bond angle (X=C, N). Our study predicts accurate theoretical reference spectra for the azine family and provides useful information on the properties of the core-ionized states as influenced by the structural change of CH↔N replacement.

The dicobalt complex [Co-2(L-2)] of a Schiff-base pyrrole macrocycle adopts a Pacman structure in solution and the solid state and shows much greater catalytic activity and selectivity for the four-electron oxygen reduction reaction (ORR) than the mononuclear cobalt phthalocyanine (CoPc) counterpart. Soft X-ray absorption spectroscopy (XAS) shows that the Co center in Co-2(L-2) is of the same valence as mononuclear CoPc. However, the former complex shows higher unoccupied Co 3d density which is believed to be beneficial for electron transfers. Furthermore, the XAS data suggests that the crystal fields for Co-2(L-2) and CoPc are different, and that an interaction remains between two Co atoms in Co-2(L-2). DFT calculations imply that the sterically hindered, cofacial structure of the dicobalt complex is critical for the operation of the four-electron reaction pathway during the ORR.

We report a photoassisted method to magnetize microcrystal fullerene C-60 at room temperature by exciting it to triplet states via a proper laser radiation and then trapping the spin-polarized states under a strong magnetic field. Novel changes on Raman scattering of the C-60 microcrystals were observed in the presence and absence of the magnetic field. In particular, the Raman spectra were found to exhibit a "hysteresis" phenomenon when the external magnetic field was removed. In light of this, we propose magnetic-field-trapped Raman spectroscopy (MFTRS) and employ first-principle calculations to reproduce the Raman activities of C-60 at different states. Further, MFTRS of the fullerene is demonstrated to originate from its photoassisted magnetization (PAM). The PAM strategy enables the magnetization of materials which consist of only light elements; meanwhile, the MFTRS investigation may open a new research field in Raman spectroscopy.

Aiming at highly efficient molecular catalyts for water oxidation, a mononuclear ruthenium complex Ru-II(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and plc = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru-II(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru-II(tpy)(pic)(3) (3; tpy = 2,2':6',2 ''-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce-IV in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Rum state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was ernployed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru-III/Ru-II) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.