Fine-structure Spectra Research Articles

Effect of Identical Sets of Structural Elements of π-Conjugated Molecules on the Parameters of Intra- and Intermolecular Interaction

A comparative analysis is performed of the parameters of the Franck–Condon and Herzberg–Teller interactions that determine the shape of the fine-structure absorption and luminescence spectra of π‑conjugated molecules having the same sets of structural elements (molecular fragments). The possibility of applying a fragmentary approach to analyzing the spectra of these molecules is demonstrated.

Theoretical Spectroscopic Studies on Chemical and Electronic Structures of Selenocysteine and Pyrrolysine

The chemical and electronic structures of the 21st and 22nd proteinogenic amino acid selenocysteine (Sec), pyrrolysine (Pyl) and their derivatives (deprotonated and protonated ions) were extensively characterized for the first time. Through the fragment based step-by-step research on their potential energy surface (PES), electronic energies of the most stable conformers of Sec, Pyl and the related ions were finally determined at the advanced CBS-QB3 and DSD-PBEP86-D3(BJ)/aug-cc-pVTZ level, respectively, with the identification of many new low-energy conformers. The infrared spectra (IR) at 298 K of the most abundant conformers in different forms were scaled by comparison with the anharmonic frequency calculations and analyzed comparing with the experimental spectra of similar molecules. The characteristic soft X-ray spectra (including X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine-structure spectra (NEXAFS)) of the most stable conformers at 498 K were also simulated. Especially, the two possible protonated configurations of Pyl can be clearly distinguished by their different spectral features. Furthermore, a small binding energy intersection appeared around 293 eV at the C 1s edge between the canonical and protonated Pyl conformers, which is different from all the previous study on similar molecules. This work thus filled the gap in our knowledge by providing detailed information on the chemical and electronic structures of Sec and Pyl and will be a useful guidance for future experimental research.

Температурные и концентрационные зависимости соотношения Ландау-Плачека в водных растворах γ-пиколина

In aqueous solutions of -picoline we investigated intensity relations in components of the fine structure spectrum of molecular light scattering – Landau-Placzek ratio – in dependence on temperature and concentration. Complex dependence of the fine structure spectrum intensity distribution was observed on temperature and concentration, which is due to structural processes in aqueous solutions.

The Effect of Fluorine Substituents on the Intra- and Intermolecular Interaction Parameters of 1,4-Distyrylbenzene Molecules

We have compared and analyzed the parameters of the Franck–Condon (FC) and Herzberg–Teller (HT) interactions, which form the fine-structure spectra of stilbene, 1,4-distyrylbenzene, and tetrafluorodistyrylbenzene—compounds that are similar in their chemical structures but differ in the length of π-conjugation and in the presence of substituents in their benzene rings. The numerical values of the FC intramolecular interaction constants have been obtained, and, simultaneously, the values of the HT parameter have been found as quantitative values of the projections of the electronic transition vector of the dipole moment onto the normal vibrational coordinates. We have solved the question of transferability of these parameters in the homologous series of stilbene molecules containing the same sets of structural elements, which has made it possible to extend the use of the fragmentary approach to describe the fundamental bands of organic molecules of different homological series and to solve the problem of studying the structure of the spectra of large molecules.

Composite Si-O-metal network catalysts with uneven electron distribution: Enhanced activity and electron transfer for catalytic ozonation of carbamazepine

Electron-rich center and electron-poor center were formed around Si and metal atom linked via Si-O-metal bonding bridge in the Co-Ce doping mesoporous molecular sieves MCM-48 for catalytic ozonation of carbamazepine (CBZ). The density functional theory (DFT) calculations of Co-Ce-MCM-48 concluded that unique Co-O-Si-O-Si-O-Ce had a much lower energy gap than those of Si-O-Si-O-Si-O-Si, Co-O-Si-O-Si-O-Ce and Co-O-Si-O-Si-O-Ce. The successful immobilization of Co-Ce was verified by X-ray absorption fine-structure (XAFS), Raman and 29Si MAS-NMR spectrum. Co-Ce-MCM-48/O3 process achieved 75.6% mineralization of CBZ at 60 min by generation of reactive oxygen species (ROSs) and enhanced redox behaviors of Ce(Ⅲ)/Ce(Ⅳ) and Co(Ⅱ)/Co(Ⅲ). Two new intermediates (P13 and P14) of CBZ in Co-Ce-MCM-48/O3 were observed by DFT and LCMS/MS results. This study opened a new insight by employing an integration of theoretical and experimental techniques to elucidate the synergistic effect of uneven electrons distribution at Co-O-Si-O-Si-O-Ce and catalytic reaction pathway of CBZ.

Electronic structure of stishovite SiO2

Electronic structure calculation of the stishovite as close packing SiO2 modification was performed with the use of the linearized augmented plane wave method in framework of Wien2k code. Band diagram, total and partial density of states were calculated. X-ray emission Si K and Si L2,3 spectra characterizing valence band were obtained. By “core hole” approximation XANES Si L2,3 was calculated. X-ray stishovite spectra reveals good agreement with the experimental data. The explanations are given for the observed density of states and emission spectra fine structure features.

Near edge X-ray absorption fine structure spectra of linear n-alkanes: Variation with chain length

The effect of chain length on the carbon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of linear n-alkanes has been examined with Transition Potential Density Functional Theory (TP-DFT) calculations. Species from propane (C3H8) to n-icosane (n-C20H42) and selected longer chains were examined. This study focuses on the prominent ‘CH band’ (287–288 eV) in these NEXAFS spectra. TP-DFT calculations show that contributions from interior methylene groups (3 or more positions from the chain end) are similar, while contributions from the terminal methyl and the first methylene groups differ. The evolution of the angle dependent and Rydberg-valence mixing with chain length are also examined.

NEXAFS spectra and specific dissociation of oligo-peptide model molecules

Total-ion-yield near-edge X-ray absorption fine-structure (NEXAFS) spectra of three oligo-peptide model molecules were recorded. The NEXAFS spectra were also calculated with time-dependent density functional theory; the calculated spectra are consistent with the experimental measurements. The ionic products from core-excited molecules and their branching ratios as functions of excitation energy show branching ratios 42%-75% of dissociation of the peptide bond, especially at resonant excitations. The major destination orbitals assigned at these excitation energies show significant antibonding character along peptide bonds, which causes large probabilities of bond cleavage.

Temperature-induced molecule assembly effects on the near-edge X-ray absorption fine-structure spectra of Zn-phthalocyanine layers on Si substrates.

The molecular arrangement of vacuum thermally deposited polycrystalline Zn-phthalocyanine (ZnPc) layers on Si substrates is investigated using near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the proximity of the carbon edge at E0 = 287.33 eV. The data were collected as a function of the deposition substrate temperature TS (30, 90, 150°C) and the incidence angle θ (20°, 45°, 70°, 90°) of the synchrotron beam with respect to the sample plane. Each spectrum was analysed by mathematical simulation applying an error function for the carbon edge and a set of Voigt and (asymmetric) Gaussian functions for C1s → π* and C1s → σ* transitions of ZnPc, respectively. It turned out that part of the organic layer consists of adventitious carbon, which does not contribute to the molecular transitions of ZnPc, whereas all molecular features exhibit polarization-dependent peak areas pointing to a reasonable fraction of well-assembled molecules at any TS. The highest adventitious carbon fraction was found at TS = 30°C, whereas the highest polarization dependence was found at TS = 90°C. The calculated average molecular tilt angles for the three temperatures (30, 90, 150°C) were γ = 60.6°, 68.7° and 66.7°, respectively. If only the polarization-dependent fractions are considered, then the three samples can be mathematically described using a shared molecular tilt angle of γ= 68.7°, which corresponds to the average tilt angle of the TS = 90°C sample.

High-resolution spectral analysis of hybrid A/B-type band of 1,3-butadiene at 6.2 μm using an EC-QCL coupled with cavity ring-down spectroscopy

The fine rotational-vibrational spectra of long-chain molecules like 1,3-butadiene are very closely spaced and highly overlapped. Such investigations require high-sensitive techniques to avoid overlapping and adequate resolution to observe their fine structure spectra. In this work, we have utilized a high-resolution external cavity-quantum cascade laser at ∼6.2 μm coupled with high-sensitive cavity ring-down spectroscopy (CRDS) to determine the fine ro-vibrational spectra of 1,3-butadiene in the gas phase. We experimentally probed the hybrid A/B-type band at 1596.412 cm−1 and also calculated relevant spectroscopic parameters of 1,3-butadiene using Gaussian 16 and subsequently simulated the spectra using PGOPHER simulation. Finally, we selected a unique interference-free spectral region within the 1,3-butadiene spectrum, and performed detailed ro-vibrational study of 3 spectral lines in this region. These results are a great advance over the earlier works and provide a spectroscopic window that may enable selective and high-sensitive sensing of 1,3-butadiene in the future.

Soft X-ray Chlorine Photolysis on Chlorobenzene Ice: An Experimental and Theoretical Study.

An experimental and theoretical study of the photoinduced homolysis of the carbon-chlorine bond in an ice matrix of chlorobenzene is presented. A condensed chlorobenzene film has been grown in situ and near edge X-ray fine structure (NEXAFS) spectra were collected after exposing the condensed film to a monochromatic photon beam centered at the 2822 eV resonant excitation of chlorine and at 2850 eV. The photoabsorption to the Cl 1s → σ* and Cl 1s → π* states has been measured and the hypothesis of free radical coupling reactions was investigated via time-dependent density functional theory (TD-DFT) and complete active space self-consistent field (CASSCF) calculations. Also, potential energy pathways to the C-Cl cleavage have been obtained at the CASSCF level to the Cl 1s → σ*, 1s → π*, and 1s → ∞ states. A strong dissociative character was only found for the Cl 1s → σ* resonance.

Fine structure of spectrum of secondary electron, 5: metals and their compounds

Fine structure of spectrum of secondary electron, 5: metals and their compounds

Влияние фторзаместителей на параметры внутри- и межмолекулярного взаимодействия молекул 1,4-дистирилбензола

A comparative analysis of the parameters of the Franсk-Kondon and Herzberg-Teller interactions forming the fine-structure spectra of α, ω-tetrafluorodysterylbenzene, 1,4-distyrylbenzene and stilbene is carried out. It is shown that the introduction of fluorine substituents leads to reduce the dipole moment of the molecule, and as a result, reduces the values of the parameters of intermolecular interaction. It is concluded that the parameters of intra- and intermolecular interactions, forming the fine-structure spectra of the selected molecules, make it possible to use the fragmentary approach in the description of fundamental bands.

Properties of NTCDA Thin Films on Ag(110): Scanning Tunneling Microscopy, Photoemission, Near-Edge X-ray Fine Structure, and Density Functional Theory Investigations

It is well proven that the properties of organic/metal interfaces play an utmost role in the performance of organic devices. Here we present a study on structural and electronic properties of high-quality 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) films grown on an Ag(110) surface. High-resolution scanning tunneling microscopy and low-energy electron diffraction show the presence of two molecular domains. Density functional theory calculations indicate that the most stable location of NTCDA corresponds to anhydride oxygen attached to the Ag atoms along the [110] direction. Photoemission results of the C 1s and O 1s core levels demonstrate a strong interfacial bonding, inducing a charge transfer from the Ag metal to the molecular monolayer. An angular-dependent study of the C K-edge near-edge X-ray fine structure spectra provides detailed information concerning the evolution of the NTCDA orientation with the film thickness.

AgI-BiOI-graphene composite photocatalysts with enhanced interfacial charge transfer and photocatalytic H2 production activity

BiOI-based photocatalysts were proved to exhibit photocatalytic H2 production activity. AgI-BiOI-graphene showed better H2 production activity than BiOI and BiOI-graphene. The surface chemistry, electronic property, phase structure, morphology, optical property and photocatalytic performance of these photocatalysts were studied. The interfacial electronic states of the photocatalysts were investigated through their C K-edge near-edge X-ray-absorption fine-structure (NEXAFS) spectra. Based on the in situ NEXAFS spectra measured with and without illumination, a mechanism about the transport of photoelectron from AgI to graphene through BiOI is proposed for the photocatalytic H2 production process. The incorporation of graphene restricted the three-dimensional self-assembly of BiOI nanocrystals and led to the formation of less extensively crystallized BiOI domains through a confined-space effect. Addition of AgNO3 precursor altered the crystal structure of BiOI from flower-like to horizontally stacked flat plates. The results of NEXAFS spectra, photoluminescence spectra and photocurrent tests reveal that the improved photocatalytic activity of the AgI-BiOI-graphene photocatalyst is attributable to the interfacial interaction among AgI, BiOI and graphene, which enhanced the separation of photogenerated electrons to generate H2. AgI-BiOI-graphene photocatalyst was a stable photocatalyst for the production of H2. After three cycles, 86% activity of recycled photocatalysts was retained.

Electronic Structure Characterization of a Thiophene Benzo-Annulated Series of Common Building Blocks for Donor and Acceptor Compounds Studied by Gas Phase Photoelectron and Photoabsorption Synchrotron Spectroscopies.

The near-edge x-ray-absorption fine-structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) spectra of benzo[ b]thiophene (BBT) and dibenzothiophene (DBT) in the gas phase have been measured at the carbon K-edge and sulfur LII,III-edge regions. The assignment of the spectral features has been provided by theoretical calculations based on density functional theory (DFT) and its time-dependent generalization (TDDFT) in the linear response regime. Observed trends in computed C 1s and S 2p ionization potentials (IPs) have been rationalized in terms of both the inductive effects due to the presence of S and the increased π-electrons delocalization arising from the benzo-annulation process. The analysis of the NEXAFS carbon K-edge and sulfur LII,III-edge regions provided information on both low-lying delocalized virtual π orbitals, and higher-lying localized σ*(C-S) states. The evolution of the NEXAFS carbon K-edge spectral features along the series thiophene (T) and derivatives, BBT and DBT, is informative of a stabilizing effect due to increased aromaticity. This effect is however more pronounced in going from T to BBT compared to the introduction of a second annulated phenyl ring in DBT. The nature of the most intense sulfur LII,III-edge NEXAFS spectral features is instead conserved along the series reflecting thus the localized nature of the virtual states involved in the S 2p core-excitation process.

Extended X-ray absorption fine structure study of the Er bonding in AlNO:Erx films with x ≤ 3.6%

The structural properties of Er-doped AlNO epilayers grown by radio frequency magnetron sputtering were studied by Extended X-ray Absorption Fine Structure spectra recorded at the Er L3 edge. The analysis revealed that Er substitutes for Al in all the studied samples, and the increase in the Er concentration from 0.5 to 3.6 at. % is not accompanied by the formation of ErN, Er2O3, or Er clusters. Simultaneously recorded X-ray Absorption Near Edge Structure spectra verify that the bonding configuration of Er is similar in all studied samples. The Er-N distance is constant at 2.18–2.19 Å, i.e., approximately 15% larger than the Al-N bond length, revealing that the introduction of Er in the cation sublattice causes a considerable local distortion. The Debye-Waller factor, which measures the static disorder of the second nearest shell of Al neighbors, has a local minimum for the sample containing 1% Er that coincides with the highest photoluminescence efficiency of the sample set.

Structural characterization of Zr-doped ZnO films deposited on quartz substrates by reactive radio frequency magnetron co-sputtering

Zr-doped ZnO (Zn1−xZrxO, 0 ≤ x ≤ 0.067; ZZO) thin films were grown at room temperature by reactive radio frequency co-sputtering on quartz substrates The ZZO films have a strong preferred orientation toward the c-axis but this orientation weakened as x increased. The size of crystallites of the ZZO films decreased and the surfaces of the ZZO films smoothened as x increased. The Zn atom were divalent and slightly affected only in the c-axis. Zn K-edge X-ray absorption near edge structure (XANES) spectra of the ZZO films show that the Zn atom were divalent and slightly affected only in the c-axis. The Zr atoms were tetravalent and their K-edge XANES spectra were slight different from that of ZrO2. Polarization-dependent Zn K-edge extended x-ray absorption fine-structure (EXAFS) spectra revealed that the local structural variation was stronger along the c-axis than along other axes. The Zn atom site was well replaced by Zr atom regardless of x. Average optical transmittance in the visible region was ≥90%, and as x increased, optical band gap increased and blue-shifted.

The distribution and coordination of trace elements in Krithe ostracods and their implications for paleothermometry

The Mg and Sr content of ostracod valves have been used to reconstruct past temperature and salinity, and their stable isotopes have been used to reveal aspects of marine, lake and estuary hydrology. However, significant uncertainties surround ostracod calcification processes, the incorporation mechanisms of trace elements, and the sensitivity of proxy tracers to complex confounding factors. The valves of most ostracods are composed of micron-scale crystalline grains embedded in an organic matrix. The fine-scale geochemistry of these structures, and the nature of the influence of biological mineralisation processes on valve chemistry, remain poorly constrained. We have performed sub-micron resolution X-ray microscopy of a marine Krithe ostracod valve, and determined the chemical coordination of Mg, and the distribution of Mg, Na and S throughout the crystal-organic valve structure. These trace elements display systematic sub-micron-scale compositional variations within the mineral grains and inter-granular matrix of the valve ultrastructure. These patterns imply that Krithe biomineralisation processes significantly modulate trace element incorporation at the sub-micron scale. Thus Krithe chemical composition is likely to be decoupled to some extent from the water in which they calcified. Most importantly, Mg K-edge Near-Edge X-Ray Absorption Fine Structure (NEXAFS) spectra, and the coincidence of high-Mg regions with S-rich organic layers reveal that Mg is not primarily hosted in the calcite structure in the valve. Our results highlight the need to understand the processes that drive this fine-scale chemical heterogeneity and their influence on connections between the external environment and valve geochemistry, if ostracods are to be used as sources of paleoenvironmental proxies.

Experimental and Theoretical Studies of the Near Edge X-ray Absorption Fine Structure Spectra and Dominant Nanoelectronic Transport Process in Organic Molecules

Experimental and Theoretical Studies of the Near Edge X-ray Absorption Fine Structure Spectra and Dominant Nanoelectronic Transport Process in Organic Molecules