Electronic Spectra Research Articles

State-selective dissociative double ionization of CH3I and CH2I2 via I 4d core-hole states studied by multi-electron-ion coincidence spectroscopy.

The dissociative double ionization of CH3I and CH2I2 irradiated with extreme ultraviolet light at hv = 100eV is investigated by multi-electron-ion coincidence spectroscopy using a magnetic bottle type electron spectrometer. The spin-orbit state-resolved Auger electron spectra for the I 4d core-hole states, (I 4d3/2)-1 and (I 4d5/2)-1, provide clear identifications of electronic states of CH3I2+ and CH2I22+. The dominant ion species produced after the double ionization correlate with the Auger electron energy, showing that different fragmentation pathways are open depending on the electronic states populated by the Auger decay. Theoretical calculations are performed to understand the fragmentation from the doubly charged states and the observed spin-orbit specificity in the Auger decay.

Excited-state properties of Cu-TADF complexes: A density functional theory study

Organometallic complexes, including copper atom, have attracted great interest as thermally activated delayed fluorescence (TADF) emitters for light emitting diode (LED) applications. This is ascribed to the potential low-cost, abundant availability of copper and most importantly to the ability of copper to enhance the spin–orbit couplings and, consequently, increase the reverse intersystem crossing rates. In this article, we use density functional theory (DFT) to investigate the excited state properties of six copper complexes based on N-heterocyclic carbene ligand, monoamido-amino carbene and diamido carbene, and carbazole ligand. The DFT calculations show that the lowest excited states consist of three groups, i.e., (i) local carbazole excitations, (ii) carbazole-to-carbene intramolecular charge transfer states, and (iii) metal-to-ligand charge transfer states. Only the latter states are characterized with large spin–orbit couplings. The DFT calculations show that the surrounding medium could have a major effect on electronic spectrum by reordering the states. Our results suggest that the TADF properties of the investigated complexes can be affected by the chemical structure of the ligands as well as by the dielectric properties of the LED device active layer.

Investigation of the Dyeing Ability of Some Reactive Triazine Azo Dyes Containing Pyrazole Fragment.

The IR, 1H NMR, and DFT studies indicated that the prepared reactive disperse dyes predominately exist as hydrazone tautomers. The electronic absorption spectra in methanol were observed and compared to those computed using B3LYP/6-311G(d,p). The dyeing efficiency of the produced dispersed reactive dyes was examined on polyester, cotton, and polyester/cotton blended fabrics. The degree of exhaustion and the quick properties of the dyed samples in terms of perspiration, washing, scorch and light fastness were assessed. It was found that reactive disperse dyes under investigation have a higher affinity for dyeing polyester textiles than cotton textiles. Moreover, the reflectance and color strength of the synthesized dyes were measured and discussed.

Enantioselective high-performance liquid chromatographycombined with spectroscopic methods and theoretical calculations: A valid strategy to determine the absolute configuration of eugenol derivatives.

The absolute configuration of three chiral eugenol derivatives was assigned by a multi-step methodology based on enantioselective HPLC combined with spectroscopic and theoretical calculations. Milligram amounts of enantiopure forms used for stereochemical characterization were isolated by HPLC on the immobilized amylose-based chiral stationary phase Chiralpak IG using normal phase elution conditions. The absolute configuration was indirectly determined for one of the three compounds by 1H NMR via methoxy-α-trifluoromethyl-α-phenylacetic acid derivatization (Mosher's acid). Comparison of the experimental and predicted electronic circular dichroism spectra confirmed the stereochemical assignment by Mosher's method and extended the absolute configuration assignment to two other chiral compounds.

Temporal and Spatial Variability of the Electron Environment at the Orbit of Ganymede as Observed by Juno

AbstractThe thermal and energetic electrons along Ganymede's orbit not only weather the surface of the icy moon, but also represent a major threat to spacecraft. In this article, we rely on Juno plasma measurements to characterize the temporal and spatial variability of the electron environment upstream of Ganymede. In particular, we find that electron spectra observed by Juno have fluxes larger by a factor of 2–9 at energies above 10 keV than what was measured two decades earlier by Galileo. This result will advance our understanding of the surface weathering and may be a concern for the radiation safety of the JUICE mission. Furthermore, the June 2021 close fly‐by of Ganymede through the moon's wake reveals that the open field line regions of its magnetosphere attenuate electron fluxes at all energies by a factor of 1.6–5, thereby offering a natural shelter to visiting spacecraft crossing this region.

Identification of cholesterol in different media by using the FT-IR, FT-Raman and UV–visible spectra combined with DFT calculations

In this investigation, the experimental FT-IR and FT-Raman spectra of cholesterol in the solid phase and in ethanol solution have been combined with the B3LYP/6–311++G** calculations and the scaled quantum mechanical force field (SQMFF) methodology, normal internal coordinates and transferable scaling factors to obtain the complete vibrational assignments of 216 vibration modes expected. Hence, complete vibrational assignments for that steroid of greatest biological importance are reported for first time in gas phase and ethanol solution together with its scaled force constants. Changes in the positions of some bands and in force constants values are observed in the different media due to the predicted intra-molecular interactions between CH3/CH3, CH3/CH2 and CH2/CH2 groups by atoms in molecules (AIM) calculations. The 1H- and 13C NMR chemical shifts of normal and deuterated cholesterol in aqueous solution confirm that the H atom of OH group is involved in the formation of H bonds in solution. Studies of experimental electronic spectra of cholesterol in different concentrations of ethanol revealed that the positions of peaks maxima increase conform increase the solution concentration. The natural bond orbital (NBO) analyses reveal that the polar OH group and the four fused rings play important roles in the stability and properties of cholesterol than the large hydrophobic moiety. Frontier orbitals predicted low reactivity of cholesterol in ethanol probably due to its high ω value in this medium.

The effect of the number of conjugated C=C bonds on the ESIPT and ICT reactions of SNCN derivatives

The electronic structure of the molecule is significantly influenced by the number of conjugated C=C bonds. In this work, the influence of the conjugated C=C bonds of the SNCN derivatives on the excited state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) properties are studied by density functional theory (DFT) and time-dependent density functional theory (TDDFT). The calculation level is proved to be reasonable by calculating electronic spectra. The hydrogen bond parameters, infrared vibrational frequency (IR), reduction density gradient (RDG) isosurface, topological analysis and potential energy curves of SNCN derivatives in ground state (S0) and the first excited state (S1) are analyzed. According to theoretical research results, ESIPT reaction has a higher likelihood of occurring in the S1 state. Moreover, the ESIPT reaction becomes more challenging to occur with the number of conjugated C=C bonds rising. Finally, the analyses of the frontier molecular orbitals (FMOs), dipole moment and charge transfer transition confirm that the ICT effect is aided by the increased number of conjugated C=C bonds. This work indicates that the number of conjugated C=C bonds can regulate the ESIPT and ICT processes, which provides guidance for the study of fluorescent groups with similar characteristics.

Energy Dissipation of Fast Electrons in Polymethylmethacrylate: Toward a Universal Curve for Electron-Beam Attenuation in Solids between ∼0 eV and Relativistic Energies.

Spectroscopy of correlated electron pairs was employed to investigate the energy dissipation process, as well as the transport and the emission of low-energy electrons on a polymethylmethacrylate surface, providing secondary electron spectra causally related to the energy loss of the primary. Two groups are identified in the cascade of slow electrons, corresponding to different stages in the energy dissipation process. The characteristic lengths for attenuation due to collective excitations and momentum relaxation are quantified for both groups and are found to be distinctly different: λ_{1}=(12±2) Å and λ_{2}=(62±11) Å. The results strongly contradict the commonly employed model of exponential attenuation with the electron inelastic mean free path as characteristic length, but they essentially agree with a theory used for decades in astrophysics and neutron transport, albeit with characteristic lengths expressed in units of angstroms rather than light-years.

Synthesis, characterization and antibacterial studies of ciprofloxaci-imines and their complexes with oxozirconium(IV), dioxomolybdenum(VI), and dioxotungsten(VI)

We synthesized and characterized ciprofloxacin-imine complexes, generated from ciprofloxacin and either 4-nitro-1,2-phenylenediamine (NO2PD) or 1,3-propanediamine (PD), in conjunction with zirconyl nitrate dihydrate, sodium molybdate dihydrate, and sodium tungstate dihydrate. Characterization involved numerous analytical methods, containing melting point determination, conductance dimensions, elemental analysis (CHN), metal content determination (%), infrared, electronic spectra, nuclear magnetic resonance, and mass spectrometry. Our findings reveal that the ligand as functions a tetra-dentate chelate binding to metal ions via azomethine and deprotonated carboxylate group. Additionally, the complexes and ligands were tested in contradiction of two types of bacteria (Staphylococcus aureus, Bacillus subtilis) and all prepared compounds showed good spectrum activity. KEY WORDS: 4-Nitro-1,2-phenylenediamine, Ciprofloxacin-imine, In-vitro antimicrobial activity, Zr complexes Bull. Chem. Soc. Ethiop. 2024, 38(4), 949-962. DOI: https://dx.doi.org/10.4314/bcse.v38i4.11

Synthesis, characterization, and antibacterial studies of some of first transition series metals and zinc complexes with mixed ligands of trimethoprim-isatin and nitrogen base

Complexes of mixed-ligand Schiff bases [trimetho-prim (TMP) with isatin] (L1) and nitrogen bases [2,2′-bipyridine (bipy)] (L2), [1,10-phenanthroline (phen) (L3)] with metal chlorides: M = Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+ were prepared and characterized by metal content determination (%), FT-IR, electronic, nuclear magnetic resonance, mass spectroscopy, magnetic susceptibility, conductance measurements and elemental analysis (CHN). The bacterial activity of the ligands and their metal compounds was evaluated via various microorganisms. Infrared spectra of Schiff base showed an azomethine peak shifted in complexes that coincide synthesis and coordination of Schiff base through the nitrogen atom of azomethine C=N) and the oxygen atom of the carbonyl group of L1 with metal ions. L2, L3 (bipy, phen) coordinated through the di imine nitrogen atoms. Conductance dimensions suggested the non-conductance nature of all the compounds except Cr(III) complexes, this outcome fits in with the molar conductance value estimated for 1:1 electrolyte in DMF. Magnetic susceptibility analysis and electronic spectra indicated an octahedral geometry for all complexes. Biological study for prepared compounds have been evaluated towards pathogenic microbes Staphylococcus aureus and Bacillus subtilis. Some compounds have stronger antibacterial action than Schiff base towards tested microbes. KEY WORDS: Antimicrobial, Heterocyclic compounds, Schiff base, Trimethoprim drug, 2,2-Bipyridyl, 1,10-Phenanthroline Bull. Chem. Soc. Ethiop. 2024, 38(4), 1013-1025. DOI: https://dx.doi.org/10.4314/bcse.v38i4.16

Chiroptical Properties of a Cryptophane Soluble at Neutral pH

AbstractThis article reports the synthesis of the two enantiomers of a water‐soluble cryptophane 3 enabling cesium and thallium complexation at neutral or basic pH. The two enantiomers of 3 were obtained in a two steps synthesis from cryptophane 4, a molecule decorated with three phenol groups and three other phenol groups protected by benzyl units. The two enantiomers of 4 were isolated from liquid chromatography using chiral stationary phase. The absolute configuration of the two enantiomers of 3 was determined by vibrational circular dichroism combined with theoretical calculations. Contrary to cryptophane 1 that present large spectroscopic changes upon cesium and thallium complexation, the electronic circular dichroism spectra of compound 3 exhibit moderate spectral changes suggesting that this compound cannot change the conformation of its linkers as easily as cryptophane 1.

Synthesis, Crystal Structure, Hirshfeld Surface, Energy Frame Work and DFT Analysis of Ethyl-4-aminobenzoate Oxalate Monohydrate Salt

Using the single crystal X-ray diffraction method, the title molecule ethyl-4-aminobenzoate oxalate monohydrate has been synthesized, crystallized and characterized. The Hirshfeld surfaces computational approach was used to analyze the intermolecular interactions in the crystal structure. The aforementioned compound crystallizes in a monoclinic crystal system of space group P21/c with the following cell parameters: a = 15.475(3), b = 5.7117(9), c = 14.029(3), = 101.764(6)º, V = 1214.0(4) 3 and Z = 4. The molecules in the crystal structure are connected by the N1-H1C···O7, O5-H2···O3, O7-H1···O4 and C8-H8A···Cg type intermolecular interaction, where Cg is the centroid of the ring. For the title molecule, the inter contact O···H (48.4%) contributes more to the Hirshfeld surfaces. The proton transfer from oxalic acid’s phenolic group to ethyl-4-aminobenzoate’s amine group, which results in the creation of salt, is revealed by the crystal structure. The ground state of ethyl-4-aminobenzoate oxalate monohydrate was also studied theoretically using the density functional method (DFT/B3LYP) with a basis set of 6–311++G(d,p). Charge transfer happens within the molecule, as shown by the computed HOMO and LUMO energies, DOS and MESP, as well as by the optimized molecular structure, electronic structural analysis and UV spectrum analysis.

Quantum radiation reaction spectrum of electrons in plane waves

In previous works we derived equations for the average momentum of high-energy electrons experiencing quantum radiation reaction in strong electromagnetic plane-wave background fields. In this paper we derive similar equations for the momentum spectrum. We formulate the equations in terms of the cumulative function and study the relation between the equations for the spectrum and the equations for the moments, analyze the structure of the low-energy expansions, and finally explain how our formulation is essentially in terms of a “Green’s function” which allows us to study the dynamics without choosing a specific initial wave packet (or particle-bunch distribution). Published by the American Physical Society 2024

Theoretical study on the effects of substituents and solvent polarity on the ESIPT properties and electronic spectra of 2-((E)-(naphthalene-3-ylimino)-methyl) phenol derivatives

In this work, the excited state intramolecular proton transfer (ESIPT) properties of the 2-((E)-(naphthalene-3-ylimino)-methyl) phenol (NMP) derivatives (NMP-NH2, NMP-OMe) in different solvents are investigated by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The results indicate NMP-OMe is more inclined to undergo the ESIPT process among the two derivatives, and the greater the polarity of solvent, the more likely the ESIPT process is to take place. Meaningfully, the two derivatives can generate the fluorescence spectra from the blue region (548 nm) to orange region (628 nm).

Fluorescent response mechanism based on ESIPT and TICT of novel probe H2QJI: A TD-DFT investigation

Recently, synthesized N-linked-disalicylaldehyde H2QJI probes have been used to detect heavy metal ions in the experiment conveniently. Nevertheless, there needs to be a more in-depth examination of the excited state intramolecular proton transfer (ESIPT) mechanism and photophysical properties of the probe. This work remedied it based on quantum chemistry calculations. We contained due hydrogen bond (O1-H2 ⋯ N3 and O4-H5 ⋯ O6) and then analyzed bond parameters, IR vibration spectra, and non-covalent interaction. The bond strength is enhanced under photoexcitation, and the former is significantly stronger. The calculated electron spectra are in agreement with the experimental values. The results of the S0 and S1 potential energy curves and IRC calculations also confirm the unique ESIPT behavior, which isan excited stated stepwise double proton transfer. The fluorescence, internal conversion, and intersystem crossing rate of KD molecules (twisted-, double proton transfer) were calculated respectively to reveal the radiative and non-radiative pathways. It proved that the corresponding spectra are not obtained since the electrons are mainly deactivated by the ISC (S1->T1). Furthermore, the interfragment charge transfer (IFCT) approach indicates that the molecule possesses twisted intramolecular charge transfer (TICT) characteristics, which lead to the quenching of fluorescence introduction.

Investigation of the structural and optoelectronic characteristics in coumarin-based dye-sensitized solar cells, both in isolation and with TiO2 adsorption

In this study, six novel organic dyes derived from coumarin have been formulated by limiting the rotation of bithiophene through the introduction of substituents, namely NCH3, Si(CH3)2, C(CH3)2, C=C(CH3)2, and C=O. Their structural, electronic, photovoltaic, and spectral properties were investigated using density functional theory at the B3LYP/6-31G(d,p) level. Furthermore, the time-dependent DFT (TD-DFT) at TD-BHandH/6-31G(d,p) level method was chosen to calculate the electronic absorption spectra and charge transfer characteristics of the investigated dyes in the chloroform solvent, as well as molecular properties such as geometries parameters, optoelectronic properties, and frontier molecular orbitals. With our studies, we reveal that all the studied dyes show significance in the range of 340.97–610.89 nm, with a band gap in the range of 1.90–2.26 eV, as well as high light capture efficiency (LHE) and significant intramolecular charge transfer (ICT) properties. In addition, we were interested in the energetic, electronic, and absorption studies of dyes linked to the TiO2 semiconductor (Dye@TiO2). All designed dyes exhibit better geometric and optoelectronic properties except for D3, which has the lowest gap energy and extends towards the red. The results reveal that these compounds would be used as potential sensitizers for DSSC applications.

Manganese 11 Complexes of Salycilhydroxamix Acid with Aniline and Ammonia with Its Properties the Effect on Microorganism

The salicylichyroxamic acid (SHA) its complex of Mn (II) along with their mixed ligand complexes of ammonia and aniline were prepared in high yields. Both the ligands and complexes were both soluble in methanol, DMSO but are insoluble in chloroform and distilled water. Their melting point were high and falls between 1910C - 400 0C. The IR spectra of the synthesized compound showed the coordination of the ligand through the oxygen of the phenolic NOH and C=O functional groups to the metals. The electronic spectra of the complexes in methanol showed some observable absorption bands of the following transitions; for Mn(SHA) complex transition is at 6A1g(s)→ 4T2g, that of Ammonia mixed complex 6A1g(s)→ 4T2g and that of Aniline mixed complex 6A1g(s)→ 4T2g. All the transitions were in the range of those observed for octahedral complexes. The antimicrobial activity of the ligand SHA (C7H7NO3), the complexes and reference drug was study against two bacterial species staphylococcus auerus and Escherichia coli, and one fungi species candida albicans. This was done using agar disc diffusion method measuring the diameter of inhibitions zone for each compound. The Mn (II) complexes produced in this study showed significant activity against the used micro-organisms. Therefore, they have potential application as anti-microbial agent.

Modeling of electronic spectra and optical responses of a semiconductor AlGaAs/GaAs quantum well with three-step barriers: the role of external perturbations and impurity

Modeling of electronic spectra and optical responses of a semiconductor AlGaAs/GaAs quantum well with three-step barriers: the role of external perturbations and impurity

Relationship between Structure and Zero-Field Splitting of Octahedral Nickel(II) Complexes with a Low-Symmetric Tetradentate Ligand

Octahedral nickel(II) complexes are among the simplest systems that exhibit zero-field splitting by having two unpaired electrons. For the purpose of clarifying the relationship between structure and zero-field splitting in a low-symmetric system, distorted octahedral nickel(II) complexes were prepared with a tetradentate ligand, 2-[bis(2-methoxyethyl)aminomethyl]-4-nitrophenolate(1−) [(onp)−]. The complex [Ni(onp)(dmso)(H2O)][BPh4]·2dmso (1) (dmso = dimethyl sulfoxide) was characterized as a bulk sample by IR, elemental analysis, mass spectrometry, electronic spectra, and magnetic properties. The powder electronic spectral data were analyzed based on the angular overlap model to conclude that the spectra were typical of D4-symmetric octahedral coordination geometry with a weak axial ligand field. Simultaneous analysis of the temperature-dependent susceptibility and field-dependent magnetization data yielded the positive axial zero-field splitting parameter D (H = guβSuHu + D[Sz2 − S(S + 1)/3]), which was consistent with the weak axial ligand field. Single-crystal X-ray analysis revealed the crystal structures of [Ni(onp)(dmso)(H2O)][BPh4]·dmso (2) and [Ni(onp)(dmf)2][BPh4] (3) (dmf = N,N-dimethylformamide). The density functional theory (DFT) computations based on the crystal structures indicated the D4-symmetric octahedral coordination geometries with weak axial ligand fields. This study also showed the importance of considering g-anisotropy in magnetic analysis, even if g-anisotropy is small.

Cascade energy reemission by the iodine atom irradiated by 0.01–100 keV photons. Role of photo- and cascade-produced electrons in radiosensitization using iodine-containing agents

Cascade decays of single K to O vacancies in an isolated iodine atom are simulated by straightforward construction of the cascade decay trees. Cascade-emitted electron and photon spectra are calculated and analyzed to determine the portions of energies (a) absorbed by the iodine atom after ionization and complete cascade relaxation, (b) emitted by cascade electrons, (c) emitted by cascade photons. These quantities are calculated as functions of incident photon energy following photoionization of the iodine atom in the 0.01–100 keV energy range. Cascade electrons and photoelectrons are shown to be principal energy transmitters from an ionized iodine atom to the environment. Presented data are relevant for developing the strategies of photon activation radiation therapy when iodine is used as a radiosensitizing agent.