Probing Rapidly‐Ionizing Super‐Atom Molecular Orbitals in C60: A Computational and Femtosecond Photoelectron Spectroscopy Study

Super‐atom molecular orbitals (SAMOs) are diffuse hydrogen‐like orbitals defined by the shallow potential at the centre of hollow molecules such as fullerenes. The SAMO excited states differ from the Rydberg states by the significant electronic density present inside the carbon cage. We provide a detailed computational study of SAMO and Rydberg states and an experimental characterization of SAMO excited electronic states for gas‐phase C₆₀ molecules by photoelectron spectroscopy. A large band of 500 excited states was computed using time‐dependent density functional theory. We show that due to their diffuse character, the photoionization widths of the SAMO and Rydberg states are orders of magnitude larger than those of the isoenergetic non‐SAMO excited states. Moreover, in the range of kinetic energies experimentally measured, only the SAMO states photoionize significantly on the timescale of the femtosecond laser experiments. Single photon ionization of the SAMO states dominates the photoelectron spectrum for relatively low laser intensities. The computed photoelectron spectra and photoelectron angular distributions are in good agreement with the experimental results.     

Photoelectron spectra of group V compounds. The elements: Sb4

The high-temperature He I photoelectron (PE) spectrum of gaseous Sb₄ is presented and assigned on the basis of the known PE ionisation energies of As₄ and P₄ and from SCC Xa eigenvalues and eigenvectors. Implications for the PE spectra of related antimony compounds are discussed.     

HeI photoelectron spectroscopic (PES) studies of the electronic structure in ω-heterocycle α-cyano polyenic ethyl ester Compounds

Hel photoelectron spectra of ω-heterocycle α-cyano polyenic ethyl ester compounds (1–6) have been given in this paper. Assignment of the spectra is also done with the aid of HeI photoelectron spectroscopic (PES) results of smaller molecules which have similar atomic group to the molecules studied, and the aid of MNDO molecules orbital calculations. The lowest PES experimental ionization potentials (IPs in eV) of different molecules reduce gradually with the increasing number of ethylenic group. The -CO₂C₂H₅ group can be only considered as a substituent.     

Photoelectron spectrum of NO2−: SAC-CI gradient study of vibrational-rotational structures

Three-dimensional accurate potential energy surfaces around the local minima of NO₂⁻ and NO₂ were calculated with the SAC/SAC-CI analytical energy gradient method. Therefrom, the ionization photoelectron spectra of NO₂⁻, the equilibrium geometries and adiabatic electron affinity of NO₂, and the vibrational frequencies including harmonicity and anharmonicity of NO₂⁻ and NO₂ were obtained. The calculated electron affinity was in reasonable agreement with the experimental value. The SAC-CI photoelectron spectra of NO₂⁻ at 350 K and 700 K including the rotational effects were calculated using the Franck–Condon approximation. The theoretical spectra reproduced well the fine experimental photoelectron spectra observed by Ervin et al. (J. Phys. Chem. 1988, 92, 5405). The results showed that the ionizations from many vibrational excited states as well as the vibrational ground state are included in the experimental photoelectron spectra especially at 700 K and that the rotational effects are important to reproduce the experimental photoelectron spectra of both temperatures. The SAC/SAC-CI theoretical results supported the analyses of the spectra by Ervin et al., except that we could show some small contributions from the asymmetric-stretching mode of NO₂⁻. © 2018 Wiley Periodicals, Inc.     

Characterization of Sb2O3 subjected to different ion and plasma surface treatments

This paper presents a study of Sb₂O₃ subjected to oxygen plasma and to ion beam bombardment (Ar⁺ and O₂⁺ ions of 4 keV) by x‐ray photoelectron and reflected electron energy‐loss spectroscopies. Changes in stoichiometry (i.e O/Sb ratio) and oxidation state of Sb have been detected and correlated with the chemical and ballistic effects of the beams used for alteration of the Sb₂O₃ surface. Thus, oxygen plasma treatments lead to a significant oxidation of the surface layers of this material with the formation of up to 51% Sb⁵⁺ species as found by Sb 4d curve‐fitting analysis. By contrast, O₂⁺ ion bombardment only produces a mild oxidation of the target with the formation of ～13% Sb⁵⁺ species. Argon ion bombardment induces a complex process where Sb⁵⁺ and Sb⁰ species are formed simultaneously. This result has been discussed in terms of a disproportionation reaction of the type Sb³⁺ → Sb⁵⁺ + Sb⁰. The changes in the electronic properties of the treated material are consistent with the loss upon oxidation to Sb⁵⁺ of the valence states associated to the 5s² electron pair of antimony. Approximate shapes of valence bands for Sb₂O₃ and Sb₂O₅ pure compounds have been extracted by applying factor analysis to valence band spectra of Sb₂O₃ subjected to different ion and plasma treatments. Copyright © 2003 John Wiley & Sons, Ltd.     

Spectroscopic properties of the methyl radical calculated from UHF SCEP wavefunctions

The potential energy surface of symmetric stretching and out-of-plane bending motions for the methyl radical has been calculated from UHF SCEP wavefunctions. Anharmonic vibrational frequencies are computed by a variational method and transition dipole moments and Einstein coefficients of spontaneous emission are reported. Isotropic hyperfine coupling constants are obtained in agreement with experiment to within 4% when calculated by differentiation of the perturbed CEPA-1 energy and taking vibrational averaging into account. Also, the temperature dependence of the proton hyperfine coupling constant compares well with experimental results. The vibrational fine structure of the first band of the photoelectron spectra of CH₃ and CD₃ is calculated in good agreement with experiment.     

Der Chemische Transport von Sb2S3 mit J2

The Chemical Transport of Sb₂S₃ With I₂ The chemical transport of Sb₂S₃ with iodine is discussed on thermodynamical basis under consideration of the gaseous molecules I₂, I₁, SbI₃, S₂, S₃, S₄, S₅, S₆, S₇ and S₈. The experiments are in a satisfying agreement with the calculations.     

First principles prediction of the elastic,electronic, and optical properties of Sb2S3 and Sb2Se3 compounds

We have performed a first principles study of structural, mechanical, electronic, and optical properties of orthorhombic Sb₂S₃ and Sb₂Se₃ compounds using the density functional theory within the local density approximation. The lattice parameters, bulk modulus, and its pressure derivatives of these compounds have been obtained. The second-order elastic constants have been calculated, and the other related quantities such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work. The linear photon-energy dependent dielectric functions and some optical properties such as the energy-loss function, the effective number of valence electrons and the effective optical dielectric constant are calculated. Our structural estimation and some other results are in agreement with the available experimental and theoretical data.     

The infrared spectra of polycyclic aromatic hydrocarbons containing a five-membered ring: symmetry breaking and the B3LYP functional

The infrared spectra of six molecules, each of which contains a five-membered ring, and their cations are determined using density functional theory; both the B3LYP and BP86 functionals are used. The computed results are compared with the experimental spectra. For the neutral molecules, both methods are in good agreement with experiment. Even the Hartree–Fock (HF) approach is qualitatively correct for the neutral species. For the cations, the HF approach fails, as found for other organic ring systems. The B3LYP and BP86 approaches are in good mutual agreement for five of the six cation spectra, and are in good agreement with experiment for four of the five cations where the experimental spectra are available. It is only for the fluoranthene cation where the BP86 and B3LYP functionals yield different results; the BP86 approach yields the expected C _{2 v} symmetry, while the B3LYP approach breaks symmetry. The experimental spectra support the BP86 spectra over the B3LYP spectra, but the quality of the experimental spectra does not allow a critical evaluation of the accuracy of the BP86 approach for this difficult system. Received: 9 February 1999 / Accepted: 31 March 1999 / Published online: 14 July 1999     

Spectroscopic investigation (IR and NMR) and HOMO-LUMO analysis of aromatic imines using theoretical approach

In this work, the theoretical studies on the structure, FT-IR, NMR, and UV–Vis spectroscopy of (E)-N-benzylidenebenzenamine (A1) and (E)-N-(2, 4′-dichlorobenzylidene) propan-1-amine (A2) are presented. The optimized structure of the molecules, NMR and UV–Vis spectra analysis were determined by the Density Functional Theory (DFT) method using B3LYP/6-311G (d, p) basis set. For FT-IR analysis, both the HF and DFT methods were used in order to determine their accuracy and reliability in theoretical calculations. The computed result of DFT calculations in comparison with the experimental results showed that the DFT method gives a more accurate prediction. The infrared (IR) spectra for the imine molecules have been recorded in the region of 500–4000 cm^?1. The gauge-independent atomic orbital (GIAO) method has been used to evaluate the ¹³C and ¹H nuclear magnetic resonance (NMR) chemical shifts of the molecules. The computed results of NMR spectra of the molecules was found to be in good agreement with the experimental data. The UV–Vis spectra of the molecules were computed to determine the HOMO-LUMO energies in order to gain insight into their electronic properties. Mulliken population analysis on atomic charges of the molecules was also calculated using the HF (Hartree-Fock) and B3LYP method. All the computed results indicated that the B3LYP method provides satisfactory results and, therefore, can be employed to support experimental data. It also demonstrated a reliable approach towards characterization of molecules in chemical science.     

UVPES of some aliphatic azides. Part I

Ab-initio calculations for ethyl azide-CH₃CH₂N₃- and azidoacetone-N₃CH₂COCH₃-were performed with the aim of interpreting their ultraviolet photoelectron spectra. Some preliminary results are presented. The first bands of the photoelectron spectra of the azides under study are intense and sharp indicating ionization from a non-bonding orbital. This is in accordance with the performed calculations, which also predict a non-bonding character to the molecular orbitals corresponding to the first ionization energies. Good agreement was also found when comparing the second ionization energies given by the calculations with the second bands of the photoelectron spectra of the molecules.     

Observation of Sb2O3 Nanocrystals in SiO2 after Sb Ion Implantation

 Antimony nanocrystals were formed in thin SiO₂ films using low-energy ion implantation of Sb followed by annealing. Using Fourier transform laser microprobe mass spectrometry (FT LMMS), we observed for the first time the presence of antimony oxide in the intermediate phase (as-implanted layer of Sb) by means of signals referring to the intact Sb₂O₃ molecules. Only SbO⁺ fragments, but no adduct ions of Sb₂O₃ could be detected in annealed samples. The size and the distribution of the nanocrystals formed around the initial depth of implantation were studied in the as-implanted samples by high-resolution electron microscopy (HREM). The crystalline structure of these nanocrystals was also studied and the presence of antimony trioxide Sb₂O₃ in the form of valentinite was proven. After the annealing step, the implanted material had spread into a wider band. The method introduced here, based on combining TEM (transmission electron microscopy) and FT LMMS results, offers the possibility of studying the evolution of the phases in Sb nanocrystal formation.     

Li17Sb13S28: A New Lithium Ion Conductor and addition to the Phase Diagram Li2S–Sb2S3

Li₁₇Sb₁₃S₂₈ was synthesized by solid‐state reaction of stoichiometric amounts of anhydrous Li₂S and Sb₂S₃. The crystal structure of Li₁₇Sb₁₃S₂₈ was determined from dark‐red single crystals at room temperature. The title compound crystallizes in the monoclinic space group C2/m (no. 12) with a=12.765(2) Å, b=11.6195(8) Å, c=9.2564(9) Å, β=119.665(6)°, V=1193.0(2) ų, and Z=4 (data at 20 °C, lattice constants from powder diffraction). The crystal structure contains one cation site with a mixed occupation by Li and Sb, and one with an antimony split position. Antimony and sulfur form slightly distorted tetragonal bipyramidal [SbS₅E] units (E=free electron pair). Six of these units are arranged around a vacancy in the anion substructure. The lone electron pairs E of the antimony(III) cations are arranged around these vacancies. Thus, a variant of the rock salt structure type with ordered vacancies in the anionic substructure results. Impedance spectroscopic measurements of Li₁₇Sb₁₃S₂₈ show a specific conductivity of 2.9×10^?9 Ω^?1 cm^?1 at 323 K and of 7.9×10^?6 Ω^?1 cm^?1 at 563 K, the corresponding activation energy is E_A=0.4 eV below 403 K and E_A=0.6 eV above. Raman spectra are dominated by the Sb?S stretching modes of the [SbS₅] units at 315 and 341 cm^?1 at room temperature. Differential thermal analysis (DTA) measurements of Li₁₇Sb₁₃S₂₈ indicate peritectic melting at 854 K.     

DFT/TDDFT investigation of the stepwise deprotonation in tetracycline: pK<Subscript>a</Subscript> assignment and UV–vis spectroscopy

Tetracyclines are a class of derivatives of polycyclic naphthacene carboxamide, which have attracted wide interest in the pharmaceutical field for their use as antibiotics. These molecules are characterized by a substantial conformational flexibility and by the presence of different binding sites which endow tetracycline with a noticeable capability in binding biological targets. A salient property of tetracyclines is the presence of multiple acidic groups: four equilibrium constants have been measured for the fully protonated tetracycline (TCH₃ ⁺) but so far no clear information concerning the pK_as of the various sites has been reported. We present here a computational investigation on the correlation between the acid–base and the spectroscopic properties of this important class of compounds. Starting from the TCH₃ ⁺ species, the pK_a of all the possible deprotonation sites has been computed by DFT calculations. The computed pK_as nicely compare with the experimental data, within 1 pK_a unit, allowing us to individuate the products of the first deprotonation. This procedure has been iteratively repeated using as starting species the products singled out from the previous deprotonation, thus individuating the stepwise products of each deprotonation step. Then, the optical absorption spectra have been computed for all the species involved in the protonation/deprotonation equilibria, comparing the results with the experimental data. The good agreement between theory and experiment has allowed us to rationalize the correlation between the solution pH and the absorption spectra.     

Bipolar Electrochemistry Exfoliation of Layered Metal Chalcogenides Sb2S3 and Bi2S3 and their Hydrogen Evolution Applications

Efficient exfoliation and downsizing of Sb₂S₃ and Bi₂S₃ layered compounds by using scalable bipolar electrochemistry on their suspensions in aqueous media are here demonstrated. The resulting samples were characterized in detail by transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy; their electrochemistry toward hydrogen evolution was also investigated. Hydrogen evolution ability of exfoliated Sb₂S₃ and Bi₂S₃ was investigated and compared to the bulk counterparts.     

双核Pt(II)配合物的光谱结构和激发态性质的密度泛函理论研究

采用基于第一性原理的密度泛函理论对单核和双核三联吡啶Pt(II)配合物[Pt(trpy)C≡CH]^＋ (1)和[Pt(trpy)C≡ (2)的基态和激发态以及光谱性质进行了系统研究. 结果揭示了双体配合物中Pt—Pt间距离在激发态时明显短于基态时的距离, 而且双体聚合后最低能吸收和发射波长相对单体配合物发生了明显红移, 这种激发的本质被指认为是来自于[d_σ*(d_δ*π*)]的MMLCT (metal-to-metal-to-ligand charge transfer)电荷转移跃迁. 另外, 对研究的配合物, 用VWN (Vosko-Wilk-Nusair)泛函优化得到的几何和用SAOP(轨道势的统计平均)计算的光谱能量和实验值符合得很好, 能够准确反映实验现象.     

Bond functions,covalent potential curves,and the basis set superposition error

In the current practice of quantum chemistry, it is not clear whether corrections for basis set superposition errors should be applied to the calculation of potential energy curves, in order to improve agreement with experimental data. To examine this question, spectroscopic parameters derived from theoretical potential curves are reported for the homonuclear diatomics C₂, N₂, O₂, and F₂, using a configuration interaction method. Three different basis sets were used, including double zeta plus polarization, triple zeta plus double polarization, and double zeta polarization augmented by bond functions. The bond function basis sets, which were optimized in the preceding paper to obtain accurate dissociation energies, also gave the most accurate parameters. The potential curves were then corrected for basis set superposition error using the counterpoise correction, and the spectroscopic parameters were computed again. The BSSE-corrected curves showed worse agreement with experiment for all properties than the original (uncorrected) curves. The reasons for this finding are discussed. In addition to the numerical results, some problems in the application of the BSSE correction to basis sets containing bond functions are shown. In particular, there is an overcounting of the lowering due to the bond functions, regardless of which type of correction is applied. Also, genuine BSSE affects cannot be separated from energy-lowering effects due to basis set incompleteness, and we postulate that it is the latter which is strongly dominant in the calculation of covalent potential curves. Based on these arguments, two conclusions follow: (1) application of BSSE corrections to potential curves should not be routinely applied in situations where the bonding is strong, and (2) appropriate use of bond functions can lead to systematic improvement in the quality of potential curves.     

A facile route to the fabrication of morphology-controlled Sb2O3 nanostructures

We report in this paper a facile hydrothermal route for the preparation of Sb₂O₃ nanoribbons assembly with different aspect ratio and Sb₂O₃ polyhedral nanoparticles. Study indicates that the ratio of water and ethanol affects the morphology, size and crystal phase of Sb₂O₃ assembly building blocks. In a mixed alcohol and water solution, the orthorhombic Sb₂O₃ nanoribbons with a length of ～4 μm and a width of 400 nm were assembled into rod-like structures, while a length of ～3 μm and a width of 300 nm Sb₂O₃ nanoribbons were assembled into quadrangle structures with the increase of the water ratio. In the absolute alcohol solution, the cubic Sb₂O₃ particles with polyhedral morphology were formed. PL spectra indicate that the morphology strongly affects the luminescence property. The possible formation mechanisms involving the surfactant-assisted self-assembly and the confined growth were also proposed for the formation of the bundled nanoribbons and polyhedral granules, respectively.     

Colloidal Synthesis and Photophysics of M3Sb2I9 (M=Cs and Rb) Nanocrystals: Lead‐Free Perovskites

Herein we report the colloidal synthesis of Cs₃Sb₂I₉ and Rb₃Sb₂I₉ perovskite nanocrystals, and explore their potential for optoelectronic applications. Different morphologies, such as nanoplatelets and nanorods of Cs₃Sb₂I₉, and spherical Rb₃Sb₂I₉ nanocrystals were prepared. All these samples show band‐edge emissions in the yellow–red region. Exciton many‐body interactions studied by femtosecond transient absorption spectroscopy of Cs₃Sb₂I₉ nanorods reveals characteristic second‐derivative‐type spectral features, suggesting red‐shifted excitons by as much as 79 meV. A high absorption cross‐section of ca. 10⁻¹⁵ cm² was estimated. The results suggest that colloidal Cs₃Sb₂I₉ and Rb₃Sb₂I₉ nanocrystals are potential candidates for optical and optoelectronic applications in the visible region, though a better control of defect chemistry is required for efficient applications.     

Theoretical and experimental study of the reactivity of PbTe in interaction with oxygen: Effect of germanium impurity atoms

High-resolution X-ray photoelectron spectroscopy (BESSY II, Berlin) has shown that germanium atoms doped into lead telluride are the centers of the oxidation reaction with dioxygen. The structure, stability, and core-level binding energies in the reaction centers have been calculated in the framework of the cluster approach with the use of the hybrid density functional (B3LYP); i.e., theoretical X-ray photoelectron spectra have been obtained. Different variants of the attachment of one to three O₂ molecules to the Ge atom located at the surface of a crystal or in the subsurface layer have been considered. It has been shown that chemisorption leads to structures with close energies, which give rise to a set of components in the spectra with unresolvable binding energies. The calculation and experimental results are in good agreement.