Electronic Spectra Research Articles

Development of an infrared diagnostic system with multi-spectrum or high frame rate for measuring the synchrotron radiation emitted by runaway electrons on EAST

In order to meet the requirements for high frame rate and synchrotron radiation spectrum of infrared diagnostic systems when studying runaway electron, an infrared diagnostic system with multi-spectrum or high frame rate has been developed and installed on the Experimental Advanced Superconducting Tokamak(EAST) for studying the runaway electrons. It is based on a high frame rate infrared camera with a high-speed rotating filter wheel and an endoscope. The infrared camera can achieve a maximum frame rate of 120 kHz in sub-windowing mode with an image size of 64 × 2. In experiments, effective data has been obtained at a frame rate of 10 kHz and an image size of 64 × 4. This diagnostic system may become a valuable tool for studying the interaction between runaway electrons and magnetohydrodynamic instability in the future. The equipped high-speed rotating filter wheel on the camera can be utilized to capture the synchrotron radiation spectrum of runaway electrons, which has been calibrated using a blackbody furnace. The synchrotron radiation spectrum contains valuable information about runaway electrons and can be one of the important parameters for inferring their accurate distribution function in the future.

Vibrationally resolved gas-phase electronic spectrum of cryogenic protonated pentacenequinone

Vibrationally resolved gas-phase electronic spectrum of cryogenic protonated pentacenequinone

Real-Time TDDFT Using Noncollinear Functionals.

Recently, we proposed a method to generalize collinear functionals to noncollinear functionals, called multicollinear approach, which has been applied in density functional theory (DFT) and linear-response time-dependent DFT (TDDFT) for the ground state and excited states calculations, respectively. In this work, we demonstrate the application of this method in real-time TDDFT by simulating electronic absorption spectra, Rabi resonance, and precession of a two-magnetic center system. Thanks to the nonvanishing local exchange-correlation torque provided by multicollinear functionals, research into the torques in the evolution of magnetization vector is carried out, which is useful for the exploration on spin dynamics.

Synthesis and characterization of a vitamin B6-tetrazole hydrazone as a fluorescence probe for selective detection of Cd2+ and Ga3+ ions

A simple selective fluorescence probe for cadmium(II) and gallium(III) ions was designed and prepared by a reaction of hydrazone formation between pyridoxal-5′-phosphate and 5-hydrazinyl-1H-tetrazole. The probe shows an enhanced blue fluorescence in the presence of Cd2+ ions and a yellow-green fluorescence in the presence of Ga3+ ions in aqueous DMSO. The conditional stability constants and stoichiometry of the Cd2+ and Ga3+ complexes were determined using the maximum likelihood method. Gallium(III) ions form two complexes of different structures with probe in solution. The DFT quantum chemical calculations were performed for obtaining molecular structures of probe 1 and its complexes with Ga3+ and Cd2+. Simulation of electronic absorption spectra and NMR spectra by TDDFT and GIAO methods allowed to determine the structures, which was obtained. The probe demonstrated a low detection limit of 0.19 μM for Cd2+ and 0.97 μM for Ga3+, making it suitable for water analysis. This research offers important insights into the design and enhancement of fluorescence probes for the selective detection of metal ions.

Substitution of the Axial Type 1 Cu Ligand Affords Binding of a Water Molecule in Axial Position Affecting Kinetics, Spectral, and Structural Properties of the Small Laccase Ssl1.

Multicopper oxidases use Cu ions as cofactors to oxidize various substrates. High reduction potential at Type 1 Cu is considered as crucial for effective catalysis. Previous studies have shown that replacing the axial methionine ligand of the Type 1 Cu with leucine or phenylalanine leads to an increased reduction potential, but not always to higher enzyme activity. Here we present a study on six variants of the small laccase Ssl1 from Streptomyces sviceus, where the axial methionine ligand was substituted, and the effect of the axial ligand on reduction potential, activity, spectral properties and structure was investigated. Absorption, electronic circular dichroism and EPR spectra revealed the presence of a stronger coordinating axial ligand like oxygen, which influences the electronic and catalytic properties more than the nature of the amino acid side chain. The crystal structures of the Ssl1 variants were solved, which show that none of the amino acid side chains coordinate to the Cu. Instead, a water molecule is found in the axial coordination site, which support the spectroscopic data. Our findings highlight the importance of combining structural and spectroscopic methods to investigate the effect of amino acid exchange on multicopper oxidases.

Quasi-2D crystals as an electrode material for high energy storage devices

The high value of the specific surface area in quasi-2D crystals, with the possibility of a large variation of their properties due to external factors, allows us to consider them as electrode materials for supercapacitors. In order to describe the specific physical properties of such crystals due to the different types of chemical bonds in them, a model is proposed. The electronic spectrum obtained has the structure (discrete levels) + (two-dimensional bands) or (mini-bands) + (two-dimensional bands). A significant relationship between the geometrical, spectral and statistical properties of the quasi-2D crystals has been found by studying the energy density of the accumulation W within the microscopic model. Contrary to existing models, the proposed model shows that under certain conditions there are two or more optimal crystal sizes where the experimentally observed maximum energy density W is realised. The model and its qualitative conclusions should be considered as the result of a microscopic approach to the problem.

Spectroscopic signatures of the S0, S1, and D0 states of indan: An experimental and theoretical investigation

The electronic and vibrational spectra of indan were explored through the utilization of Fourier transform infrared (FT-IR) spectrum, one-color resonant two-photon ionization (1C-R2PI) spectrum, and two-color resonant two-photon ionization (2C-R2PI) slow electron velocity-map imaging (SEVI) techniques in combination with quantum chemical calculations. Experimental spectra are found to be in good overall accordance with the theoretical calculations. The vibrational modes of the S0 neutral ground state, S1 first electronic excited state, and D0 cationic ground state were assigned with the assistance of density functional theory (DFT) calculations. The S1 ← S0 electronic transition energy was determined to be 36909 ± 5 cm−1 from the one-color resonant two-photon ionization spectrum. Moreover, the adiabatic ionization energy was deduced as 68419 ± 6 cm−1 based on the SEVI spectra.

Linear Response pCCD-Based Methods: LR-pCCD and LR-pCCD+S Approaches for the Efficient and Reliable Modeling of Excited State Properties.

In this work, we derive working equations for the linear response pair coupled cluster doubles (LR-pCCD) ansatz and its extension to singles (S), LR-pCCD+S. These methods allow us to compute electronic excitation energies and transition dipole moments based on a pCCD reference function. We benchmark the LR-pCCD+S model against the linear response coupled-cluster singles and doubles method for modeling electronic spectra (excitation energies and transition dipole moments) of the BH, H2O, H2CO, and furan molecules. We also analyze the effect of orbital optimization within pCCD on the resulting LR-pCCD+S transition dipole moments and oscillator strengths and perform a statistical error analysis. We show that the LR-pCCD+S method can correctly reproduce the transition dipole moments features, thus representing a reliable and cost-effective alternative to standard, more expensive electronic structure methods for modeling electronic spectra of simple molecules. Specifically, the proposed models require only mean-field-like computational cost, while excited-state properties may approach the CCSD level of accuracy. Moreover, we demonstrate the capability of our model to simulate electronic transitions with non-negligible contributions of double excitations and the electronic spectra of polyenes of various chain lengths, for which standard electronic structure methods perform purely.

Vibronic Coupling Effects in the Photoelectron Spectrum of Ozone: A Coupled-Cluster Approach.

One of the most important areas of application for equation-of-motion coupled-cluster (EOM-CC) theory is the prediction, simulation, and analysis of various types of electronic spectra. In this work, the EOM-CC method for ionized states, known as EOM-IP-CC, is applied to the closely lying and coupled pair of states of the ozone cation─X̃2A1 and Ã2B2─using highly accurate treatments including up to the full single, double, triple, and quadruple excitations (EOM-IP-CCSDTQ). Combined with a venerable and powerful method for calculating vibronic spectra from the Hamiltonian produced by EOM-IP-CC calculations, the simulations yield a spectrum that is in good agreement with the photoelectron spectrum of ozone. Importantly, the calculations suggest that the adiabatic gap separating these two electronic states is somewhat smaller than currently thought; an assignment of the simulated spectrum together with more precise band positions of the experimental measurements suggests T00 = 1,368 ± 65 cm-1.

Vibrational Mode-Dependent Circular Dichroism of Jet-Cooled Styrene Oxide.

Vibrational mode-dependent circular dichroism (CD) effects in vibrational CD spectra are often used to determine the handedness of molecules with multiple chiral centers. Here, we investigate vibrational mode-dependent CD effects in the electronic CD spectra of jet-cooled (R)-(+)- and (S)-(-)-styrene oxide obtained by using resonant two-photon ionization CD (R2PICD) spectroscopy. Although most fundamental vibronic bands demonstrated CD signatures consistent with that of the origin band, the overtone and combination bands exhibited opposite CD signatures. Theoretical calculations suggest that CD in fundamental bands are primarily governed by Franck-Condon contributions, whereas Herzberg-Teller contributions, which reflect the influences of vibrational modes on CD values, become more significant in overtone and combination bands. These results underscore the potential of mode-dependent vibronic CD signals in R2PICD spectra for determining the absolute configurations of molecules with multiple chiral centers.

MODIFICATION OF THE METHOD OF QUANTITATIVE DETERMINATION OF FLAVONOIDS IN THE GRASS OF THE MOUNTAIN BIRD POLÝGONUM AVICULÁRE L.

Аbstract Aim– Modification a methodology of the quantitative content of the sum of flavonoids in the raw material of bird's knotweed (Polýgonum Aviculáre L.) Material and methods. The raw materials of the bird's mountaineer (grass) were collected near the village of Ponomarevka, Dombarovka, Alekseevka, Orenburg region in June-July 2022. The collected material was dried in accordance with the requirements of the GF. The quantitative content was studied using a Vilitek VBS ultrasonic bath at a temperature of 40 ° C and a power of 60 W, a LAB-TB-6/W water bath at a temperature of 90 ° C, a rotary evaporator "IR-1 LT" at a temperature of 70 ° C. The electronic spectra were measured on a UNICO 2800 UV spectrophotometer, in 10 mm thick cuvettes in the wavelength range from 190 to 700 nm. The comparison solution was prepared using 96% ethyl alcohol concentration. Results. The presented method of quantitative determination can be used in "end-to-end" standardization, for raw materials of other types of mountaineer, as well as medicinal herbal preparations based on mountaineers. We selected the extraction conditions using 50% ethyl alcohol in a ratio (raw material-extractant) of 1:50 and boiling in a water bath for 60 minutes, which allowed us to achieve the yield of the amount of flavonoids more than 0.5% declared in GF XIV (FS.2.5.0069.18). Conclusion. New, different from pharmacopoeia conditions for the analysis of the quantitative determination of the amount of flavonoids in the grass of the mountaineer bird are proposed. The main differences, which is a single extraction, in comparison with a three-stage pharmacopoeia; reduction of extraction time in a water bath to 60 minutes, which is 30 minutes less than in the method of GF XIV; the concentration of the extractant and the ratio of "raw materials:extractant". Thus, the method of quantitative determination of the grass of the mountain bird has been modified according to the basic conditions of extraction of raw materials. As a result, based on the data obtained, we can recommend the content of flavonoids in the raw material of bird's knotweed at least 1.5 ± 0.08%.

Cross Peaks on Two-Dimensional Optical Spectra Arising from Quantum Cross-Correlation Functions.

Cross peaks on 2D optical spectra are indicative of interactions between molecular excitonic states. Currently, the two conventional assignments of cross peaks are direct coupling and population transfer between excitonic states. Here, we show that there is another possible source of cross peaks. We theoretically demonstrate that for a model comprising two nondirectly interacting excitons or two-level systems (TLSs), cross peaks can arise if there is a complex-valued or quantum frequency-gap cross-correlation function between the two TLSs. Considering only real-valued or classical cross-correlation functions will result in no cross peaks. We derive and validate the mathematical expressions describing such cross peaks. We then simulate the 2D electronic spectra of an example model system comprising nondirectly interacting TLSs whose quantum cross-correlation functions arise from coupling to a common overdamped Brownian oscillator mode. We show that there are clear observational differences between such quantum correlation cross peaks with conventional direct coupling and population transfer cross peaks.

Significant Chiral Asymmetry Observed in Neutral Amino Acid Ultraviolet Photolysis.

The origin of homochirality in biological organisms remains an open question. Some suggest that its origin might be extraterrestrial, specifically due to the exposure of chiral molecules to circularly polarized photons in interstellar space, which could cause an initial population imbalance leading to the homochirality observed today. However, this extraterrestrial hypothesis has not been widely accepted, largely due to the belief that molecular optical rotatory dispersion is too insignificant to create the substantial imbalance required for homochirality. Here we report experimental evidence that specific conformers of neutral amino acids exhibit significant asymmetry in the chiral destroying dissociation rate induced by circularly polarized photons. The observed anisotropy factor for the lowest energy conformer of leucine was remarkably large, reaching 0.1─a factor of 13 times larger than observed for zwitterionic leucine in solid films, and nearly 40 times greater than the anisotropy reported in the electronic absorption spectrum of gas-phase leucine ensembles at room temperature. This significant finding indicates that even if reported anisotropy values in the electronic absorption spectrum are low, the dissociation asymmetry of certain conformers can still be substantial. An anisotropy factor of 0.1 could result in an initial enantiomeric excess exceeding 10%, even with a 90% extent of reaction. This discovery suggests that asymmetric photodissociation of amino acids may have been a crucial factor in the emergence of biological homochirality.

Low-Energy Magnetic States of Tb Adatom on Graphene.

Electronic structure and magnetic interactions of a Tb adatom on graphene are investigated from first principles using combination of density functional theory and multiconfigurational quantum chemistry techniques including spin-orbit coupling. We determine that the six-fold symmetry hollow site is the preferred adsorption site and we investigate electronic spectrum for different adatom oxidation states including Tb3+, Tb2+,Tb1+, and Tb0. For all charge states, the Tb 4f8configuration is retained with other adatom valence electrons being distributed over 5dxy, 5dx2+y2, and 6s/5d0single-electron orbitals. We find strong intra-site adatom exchange coupling that ensures that the 5d6sspins are parallel to the 4fspin. For Tb3+, the energy levels can be described by theJ= 6 multiplet split by the graphene crystal field. For other oxidation states, the interaction of 4felectrons with spin and orbital degrees of freedom of 6s5delectrons in the presence of spin-orbit coupling results in the low-energy spectrum composed closely lying effective multiplets that are split by the graphene crystal field. Stable magnetic moment is predicted for Tb3+and Tb2+adatoms due to uniaxial magnetic anisotropy and effective anisotropy barrier around 440 cm-1controlled by the temperature assisted quantum tunneling of magnetization through the third excited doublet. On the other hand, in-plane magnetic anisotropy is found for Tb1+and Tb0adatoms. Our results indicate that the occupation of the 6s5dorbitals can dramatically affect the magnetic anisotropy and magnetic moment stability of rare earth adatoms.

Ab initio calculations of molecular double Auger decay rates.

We report on the application of the recently developed Fano-ADC(2,2) method to compute total and partial Auger decay widths of molecular core-hole states, including explicit evaluation of double Auger decay branching ratios. The method utilizes the fast-convergent intermediate state representation to construct many-electron wave functions and is readily applicable to atoms, molecules, and clusters. The ADC(2,2) scheme describes the initial and final states of the normal Auger decay consistently up to the second order of perturbation theory. In addition, excitations with two electrons in the continuum provide access to three-electron decay modes. The method yields decay widths and the Auger electron spectra in excellent agreement with the experiment, demonstrating the high accuracy of partial widths. The average relative error of double Auger decay branching ratios compared to available experimental data is about 30%, which should be evaluated as an excellent result considering the universality of the method, the complexity of the double decay process, and the neglection of nuclear motion in this study.

Quasicrystalline 30° twisted bilayer graphene: fractal patterns and electronic localization properties

The recently synthesized 30° twisted bilayer graphene (30°-TBG) systems are unique quasicrystal systems possessing dodecagonal symmetry with graphene’s relativistic properties. We employ a real-space numerical atomistic framework that respects both the dodecagonal rotational symmetry and the massless Dirac nature of the electrons to describe the local density of states of the system. The approach we employ is very efficiency for systems with very large unit cells and does not rely on periodic boundary conditions. These features allow us to address a broad class of multilayer two-dimensional crystal with incommensurate configurations, particularly TBGs. Our results reveal that the 30°-TBG electronic spectrum consist of extended states together with a set of localized wave functions. The localized states exhibit fractal patterns consistent with the quasicrystal tiling.

Design of a New Catalyst, Manganese(III) Complex, for the Oxidative Degradation of Azo Dye Molecules in Water Using Hydrogen Peroxide.

In the current work, chloro(meso-tetrakis(phenyl)porphyrin) manganese(III) [Mn(TPP)Cl] was synthesized following two steps: the preparation of meso-tetraphenylporphyrin (H⁠2TPP) and the insertion of manganese into the free porphyrin H2TPP. The compounds were characterized using SEM, FT-IR, UV, TGA/DTA, and XRD analyses. Manganese(III) meso-porphyrins exhibited hyper-type electronic spectra with a half-vacant metal orbital with symmetry, such as [dπ:dxz and dyz]. The thermal behavior of [Mn(TPP)(Cl)] changed (three-step degradation process) compared to the initial H2TPP (one-step degradation process), confirming the insertion of manganese into the core of the free porphyrin H2TPP. Furthermore, [Mn(TPP)Cl] was used to degrade calmagite (an azo dye) using H2O2 as an oxidant. The effects of dye concentration, reaction time, H2O2 dose, and temperature were investigated. The azo dye solution was completely degraded in the presence of [Mn(TPP)(Cl)]/H2O2 at pH = 6, temperature = 20 °C, C0 = 30 mg/L, and H2O2 = 40 mL/L. The computed low activation energy (Ea = 10.55 Kj/mol) demonstrated the efficiency of the proposed catalytic system for the azo dye degradation. Overall, based on the synthesis process and the excellent catalytic results, the prepared [Mn(TPP)Cl] could be used as an effective catalyst for the treatment of calmagite-contaminated effluents.

Cyclometalated Iridium(III) Complex with Substituted Benzimidazole: pH Directed Organelle-Specific Localization Within Lysosome.

We report the synthesis and pH dependent emission spectral behaviour of four emissive iridium(III) complexes (Ir1-Ir4) with two isomeric pairs of bis-trifluoromethyl appended benzimidazole ligands. The imidazolyl hydrogen(N-H) has been replaced by phenyl groups (N-Ph) in two ligands to understand the impact of hydrogen bonding on the photophysical properties of the complexes and it indeed plays interesting role in the charge-transfer dynamics. The pH dependent electronic spectral change is observed for two of the complexes. The enhancement of emission intensity is observed at different wavelength for pH<7 and pH>7 for Ir1 and Ir3. The emission sensing of biogenic amines with pka values ranging from 5.80-9.74 is reported along with cellular imaging. The complex Ir1 specifically localizes within lysosome (pH=4.5-5) and thus image this organelle with great precision. The detail electronic spectra and electrochemical behaviour were reported here along with TDDFT results.

Solvents and their influence on electronic properties in IEFPCM solvation model, anticancer activity, and docking studies on (E)-2-((4-chlorobenzylidene) amino)phenol

The Schiff base (E)-2-((4-chlorobenzylidene)amino)phenol (4CL2AM) has been synthesized from 4-chlorobenzaldehyde and 2-aminophenol. Spectroscopic techniques like FTIR, Raman, UV, fluorescence, and NMR were used to characterize the synthesized compound. The experimental data well matched with the DFT method (B3LYP/cc-pVDZ basis set). The frontier molecular orbital (FMO), molecular electrostatic potential (MEP), and electronic spectra (UV–visible) analysis were conducted on three different solvents such as gas, DMSO, and water. The frontier molecular orbital (FMO) analysis calculated the HOMO-LUMO energy gap as 4.0109 eV, 4.0406 eV, and 4.0411 eV for the gas phase, DMSO, and water respectively. Molecular electrostatic potential (MEP), localized orbital locator (LOL), and electron localize function (ELF) analysis revealed positions of localized and delocalized orbitals as well as electrophilic and nucleophilic attack sites. The natural bond orbital analysis (NBO) predicted highest stabilization energy was 33.37 kcal/mol. The locations of the covalent and non-covalent interactions were investigated by density overlaps region indicator (DORI), interaction region indicator (IRI), and noncovalent interaction (NCI) analysis. Drug likeness and ADME analysis were investigated. In vitro, anticancer activity studies revealed against MCF-7 breast cancer cell lines. In the molecular docking study, the predicted lowest binding energy is −5.77 kcal/mol for the 6NLV-4CL2AM system.

Electronic structure and chemical bond in MdO2

The calculation of the electronic structure of MdO2 was carried out using the fully relativistic method of discrete variation (RDV), a scheme of molecular orbitals (MO) was built and a histogram of the spectrum of X-ray photoelectron spectroscopy (XPS) was constructed in the range of electron binding energies (BE) 0–∼40 eV. It was discovered that the complex structure of the XPS spectrum of valence electrons is associated with the formation of the outer valence molecular orbitals (OVMO, BE from 0 to ∼15 eV) and of the inner valence molecular orbitals (IVMO, BE from ∼15 to ∼40 eV). The effective charge of Md in MdO2 calculated from the MO compositions was equal to +0.50 electrons. IVMO electrons were found to weaken the bond formed by OVMO in MdO2 by ∼34%.