S 2p photoabsorption of the SF5CF3 molecule: Experiment,theory and comparison with SF6

The S 2p core excitation spectrum of the SF₅CF₃ molecule has been measured in the total ion yield mode. It resembles a lot the analogous spectrum of SF₆, also recorded in this study, displaying intense transitions to the empty molecular orbitals both below and above the S 2p ionization potential (IP) and weak transitions to the Rydberg orbitals. The S 2p photoabsorption spectra of SF₆ and SF₅CF₃ have been calculated using time-dependent density functional theory, whereby the spin–orbit coupling was included for the transitions below the S 2p IP. The agreement between experiment and theory is good for both molecules, which allows us to assign the main S 2p absorption features in SF₅CF₃.     

Anharmonicity in rotational and vibrational excitation of H2 by Li+ collisions

Integral cross sections for pure rotational and vibrational-rotational excitation of H₂(X¹Σ⁺_g) by Li⁺(¹S) impact are computed by close-coupling methods at 0.2, 0.6, and 1.2 eV in the c.m. system using vibrational functions that are numerical solutions of the one-dimensional radial Schrödinger equation for harmonic, Morse, and adiabatically corrected Kolos-Wolniewicz (KW) potential functions. Comparison of results employing KW and Morse functions shows excellent agreement for all transitions studied. Findings using harmonic oscillator functions, however, differ noticeably from KW and Morse values for vibrational (0 → 1) and very large rotational (Δj = 10) transitions, but are satisfactory for lower order (0 → 2, 4, 6, 8) rotational transitions.     

Single-Ion Magnetic Behaviour in an Iron(III) Porphyrin Complex: A Dichotomy Between High Spin and 5/2–3/2 Spin Admixture

A mononuclear iron(III) porphyrin compound exhibiting unexpectedly slow magnetic relaxation, which is a characteristic of single-ion magnet behaviour, is reported. This behaviour originates from the close proximity (≈550 cm⁻¹) of the intermediate-spin S=3/2 excited states to the high-spin S=5/2 ground state. More quantitatively, although the ground state is mostly S=5/2, a spin-admixture model evidences a sizable contribution (≈15 %) of S=3/2 to the ground state, which as a consequence experiences large and positive axial anisotropy (D=+19.2 cm⁻¹). Frequency-domain EPR spectroscopy allowed the m_S= |±1/2⟩→|±3/2⟩ transitions to be directly accessed, and thus the very large zero-field splitting in this 3d⁵ system to be unambiguously measured. Other experimental results including magnetisation, Mössbauer, and field-domain EPR studies are consistent with this model, which is also supported by theoretical calculations.     

Collision- and non-collision-induced predissociation in the appearance of S+ and CS+ ions from CS2 under electron impact

Metastable transitions in CS⁺₂ leading to S⁺ + CS and CS⁺ + S under electron impact on CS₂ ae reported. The predissociation processes able to explain the occurrence of these metastable transitions are discussed. An interpretation of some fast dissociation processes is suggested.     

High-temperature FeS-FeS2 solid-state transitions: Reactions of solid mackinawite with gaseous H2S

Phase transitions and reactions of non-oxidized and surface-oxidized mackinawite (FeS) in helium and H₂S gas were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). DFT was used to obtain optimized structures of the iron-sulfur phases mackinawite, hexagonal pyrrhotite, greigite, marcasite and pyrite and to determine the thermochemical properties of reactions of mackinawite with H₂S to these phases. The phase transitions of mackinawite to hexagonal pyrrhotite are endothermic, while reactions to greigite, marcasite and pyrite are exothermic. The experiments show that non-oxidized mackinawite converts into hexagonal pyrrhotite (Fe₉S₁₀ first and then Fe₇S₈) in He and also in H₂S but at a lower temperature. No further reactions can be observed under these conditions. In the case of surface-oxidized mackinawite, the extent of surface oxidation determines the course and the final product of the reaction with H₂S. If the extent of surface oxidation is low, only Fe²⁺ is oxidized to Fe³⁺. Under these conditions mackinawite converts into the mixed-valence thiospinel compound greigite. In case of pronounced surface oxidation all surface Fe centers are oxidized to the Fe³⁺ state and S²⁻ is oxidized to SO₄²⁻. Oxidation of sulfur is a prerequisite for the formation of pyrite.     

Über Zinn-haltige Heterocyclen. VIII. 2-Chlor-2-phenyl-1,3,6-trithia-2-stannocan Kristallstruktur und Schwingungsspektren

On Heterocyclic Systems Containing Tin. VIII. 2-Chloro-2-phenyl-1,3,6-trithia-2-stannocane, Crystal Structure and Vibrational Spectra The crystal structure of the title compound has been determined and refined until R = 0.040. The coordination around tin is trigonal bipyramidal (equatorial ligands 2 × S and Ph; axial ligands Sn? Cl 245.3(2) and 1,5-transannular Sn…?S 280.6(2) pm). The eight-membered ring has boat-chair conformation. The vibrational spectra of the title compound and of five analogues with donor O or S and substitution Cl, Ph are given and discussed. The three compounds with donor S have nearly identical aliphatic ring modes (3 × boat-chair conformation), whereas these modes exhibit a conformational change for the case of donor O in the series Cl₂, Ph₂, ClPh substituted tin. The stretching vibrations of the coordination polyhedron Cl_nSnS₂ are in the range 400 to 340 cm^?1. The strong 1,5-transannular Sn…?O or Sn…?S interactions in the cases of Cl substituted Sn are correlated with strong and broad transitions in the range 330 to 280 cm^?1; an extended distance of 5 pm is in correspondence with an approximate decrease of energy by 40 cm^?1.     

Darstellung und spektroskopische Charakterisierung der reinen Bindungsisomeren [OsCl5(NCS)]2− und [OsCl5(SCN)]2−

Preparation and Spectroscopic Characterization of the Pure Bondisomers [OsCl₅(NCS)]^2? and [OsCl₅(SCN)]^2? The oxidation of [OsCl₅I]^2? with (SCN)₂ in CH₂Cl₂ yields the bondisomers [OsCl₅(NCS)]^2? and [OsCl₅(SCN)]^2?, which are isolated as pure compounds by ion exchange chromatography on DEAE-Cellulose. Only the salts of the N-isomer show significant shifts in the vibrational and electronic spectra caused by polarization of the terminal S depending on the size of the cations and the polarity of the solvents. In the IR and Raman spectra ν_CN(S), ν_CS(N) and δ_NCS are found at higher wave numbers than ν_CN(N), ν_CS(S) and δ_SCN. In the optical spectrum of the red [OsCl₅(SCN)]^2? the charge-transfer S→Os is nearly constant at 538 nm, but the N→Os transition of the yellow to violet coloured N-isomer shifts from 480 nm in organic solvents or in presence of large alkylammonium cations to 516 nm in aqueous solution and to 544 nm in the solid Cs-salt. The optical electronegativities are calculated to χ_opt(–SCN) = 2.6 and χ_opt(–NCS) = 2.6–2.8. According to spinorbit coupling and to lowered symmetry (C_4v) the splitted intraconfigurational transitions are observed at 10 K as weak peaks in the regions 600, 1000 and 2000 nm. The O? O transitions are calculated from the vibrational fine structure. The lowest level of both isomers is confirmed by peaks in the electronic raman spectra. With the parameters ζ(Os^IV) = 3200 cm^?1 and B(? SCN) = 316 cm^?1 or B(? NCS) = 288 cm^?1 there is a good fit of calculated and experimental data, resulting in the nephelauxetic series: F^? > CI^? > SCN^? > Br^? > NCS^? > I^?.     

Temperature Dependent Excitonic Transition Energy and Enhanced Electron-Phonon Coupling in Layered Ternary SnS2-xSex Semiconductors with Fully Tunable Stoichiometry

In this study, a series of SnS_2-xSe_x (0 ≤ x ≤ 2) layered semiconductors were grown by the chemical–vapor transport method. The crystal structural and material phase of SnS_2-xSe_x layered van der Waals crystals was characterized by X-ray diffraction measurements and Raman spectroscopy. The temperature dependence of the spectral features in the vicinity of the direct band edge excitonic transitions of the layered SnS_2-xSe_x compounds was measured in the temperature range of 20–300 K using the piezoreflectance (PzR) technique. The near band-edge excitonic transition energies of SnS_2-xSe_x were determined from a detailed line-shape fit of the PzR spectra. The PzR characterization has shown that the excitonic transitions were continuously tunable with the ratio of S and Se. The parameters that describe the temperature variation of the energies of the excitonic transitions are evaluated and discussed.     

Water solvent effects using continuum and discrete models: The nitromethane molecule,CH3NO2

The first three valence transitions of the two nitromethane conformers (CH₃NO₂) are two dark n → π* transitions and a very intense π → π* transition. In this work, these transitions in gas‐phase and solvated in water of both conformers were investigated theoretically. The polarizable continuum model (PCM), two conductor‐like screening (COSMO) models, and the discrete sequential quantum mechanics/molecular mechanics (S‐QM/MM) method were used to describe the solvation effect on the electronic spectra. Time dependent density functional theory (TDDFT), configuration interaction including all single substitutions and perturbed double excitations (CIS(D)), the symmetry‐adapted‐cluster CI (SAC‐CI), the multistate complete active space second order perturbation theory (CASPT2), and the algebraic‐diagrammatic construction (ADC(2)) electronic structure methods were used. Gas‐phase CASPT2, SAC‐CI, and ADC(2) results are in very good agreement with published experimental and theoretical spectra. Among the continuum models, PCM combined either with CASPT2, SAC‐CI, or B3LYP provided good agreement with available experimental data. COSMO combined with ADC(2) described the overall trends of the transition energy shifts. The effect of increasing the number of explicit water molecules in the S‐QM/MM approach was discussed and the formation of hydrogen bonds was clearly established. By including explicitly 24 water molecules corresponding to the complete first solvation shell in the S‐QM/MM approach, the ADC(2) method gives more accurate results as compared to the TDDFT approach and with similar computational demands. The ADC(2) with S‐QM/MM model is, therefore, the best compromise for accurate solvent calculations in a polar environment. © 2015 Wiley Periodicals, Inc.     

Two-photon spectroscopy of organic molecules recorded by the fluorescence induced by a picosecond light continuum generated in D2O

It is shown that the fluorescence of large organic molecules induced by the two-photon excitation of a picosecond light continuum generated in D₂O is a useful and sensitive new technique for two-photon spectroscopic study or excited electronic states of large organic molecules in solution This technique is tested on the first two singlet transitions of rhodamine 6G and on the first singlet transitions (430–630 nm) of naphthalene.     

Theoretical study of three-body nonadditive interactions for the H2S-(H2O)2 system

An ab initio SCF MO study of the hydrogen-bonded system formed by an H₂S molecule interacting with two water molecules is presented. The nonadditive contributions to the interaction energies are obtained using the 4-31G basis sets which tend to overestimate the dipole moments of the H₂S and H₂O molecules. Thus possibly too large interactions, including upper-limit values for the nonadditive three-body contributions, were obtained. The nonadditive corrections were found to be comparable in magnitude to the cases of other first-row hydride trimers. On this basis one can infer that they probably do not affect the proton and deuterium exchange in hydrated H₂S (as occurs in the G-S heavy water enrichment process) and that they do not play an important role in the formation of clathrates involving hydrogen sulphide.     

Polymorphism in Bi2WO6

The polymorphism of Bi₂WO₆ has been studied using differential dilatometry and differential thermal analysis with polycrystalline specimens prepared by sintering the oxides Bi₂O₃ and WO₃. Two reversible polymorphic transitions were observed, one at 662°C and one at 962°C. The former transition showed a very small change of enthalpy and very little dimensional change, while the latter showed a large thermal hysteresis, had a large change of enthalpy, and was accompanied by a sizable volume change. The high-temperature powder X-ray data indicated that the intermediate phase as well as the low-temperature form had orthorhombic symmetry and the high-temperature form had monoclinic symmetry. The 662°C transition is displacive and the 962°C transition reconstructive. A crystal structure of the high-temperature form is proposed and discussed in comparison with that of the low-temperature form.     

Partial oscillator strengths for the photoionization of N2O and CO2 (20–60 eV)

The photoelectron branching ratios and the partial oscillator strengths (cross sections) for photoionisation of the valence orbitals of N₂O and CO₂ have been obtained in the energy range 20–60 eV using the magic angle dipole (e, 2e) method. In addition to single electron ionization processes there is a large contribution from multiple electron transitions at higher energies in agreement with recent theoretical predictions. The photoionization efficiency and the dipole oscillator strenght for total photoabsorption have also been measured.     

Electronic absorption spectra of V2O5

MO calculations of electronic structure and optical transitions for [VO_n]^{5 ?; 2n} (n = 4, 5, 6) clusters in V₂O₅ monocrystals have been carried out by means of the semiempirical CNDO CI method. Using the calculated results, a complete analysis of V₂O₅ optical data as available in the literature and as obtained in the electroreflectivity experiments presented in this paper is performed. An identification of optical transitions in a wide energy range is presented. The optical properties of vanadium pentoxide are shown to be due to the localized charge transfer electronic transitions in the clusters. The fine structure of optical spectra is connected with the covalent splittings of the vanadium 3d and oxygen 2p atomic levels.     

A template-free solvothermal synthesis and photoluminescence properties of multicolor Gd2O2S:xTb3+, yEu3+ hollow spheres

The multicolor Gd₂O₂S:xTb³⁺, yEu³⁺ hollow spheres were successfully synthesized via a template-free solvothermal route without the use of surfactant from commercially available Ln (NO₃)₃·6H₂O (Ln = Gd, Tb and Eu), absolute ethanol, ethanediamine and sublimed sulfur as the starting materials. The phase, structure, particle morphology and photoluminescence (PL) properties of the as-obtained products were investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectra. The influence of synthetic time on phase, structure and morphology was systematically investigated and discussed. The possible formation mechanism depending on synthetic time t for the Gd₂O₂S phase has been presented. These results demonstrate that the Gd₂O₂S hollow spheres could be obtained under optimal condition, namely solvothermal temperature T = 220 °C and synthetic time t = 16 h. The as-obtained Gd₂O₂S sample possesses hollow sphere structure, which has a typical size of about 2.5 μm in diameter and about 0.5 μm in shell thickness. PL spectroscopy reveals that the strongest emission peak for the Gd₂O₂S:xTb³⁺ and the Gd₂O₂S:yEu³⁺ samples is located at 545 nm and 628 nm, corresponding to ⁵D₄→⁷F₅ transitions of Tb³⁺ ions and ⁵D₀→⁷F₂ transitions of Eu³⁺ ions, respectively. The quenching concentration of Tb³⁺ ions and Eu³⁺ ions is 7%. In the case of Tb³⁺ and Eu³⁺ co-doped samples, when the concentration of Tb³⁺ or Eu³⁺ ions is 7%, the optimum concentration of Eu³⁺ or Tb³⁺ ions is determined to be 1%. Under 254 nm ultraviolet (UV) light excitation, the Gd₂O₂S:7%Tb³⁺, the Gd₂O₂S:7%Tb³⁺,1%Eu³⁺ and the Gd₂O₂S:7%Eu³⁺ samples give green, yellow and red light emissions, respectively. And the corresponding CIE coordinates vary from (0.3513, 0.5615), (0.4120, 0.4588) to (0.5868, 0.3023), which is also well consistent with their luminous photographs.     

Influence des substitutions sur les transitions de phases de pyrochlores derivées de Cd2Nb2O6S

This paper reports the evolution of phase transitions and ferroelectric properties of the pyrochlore type compound Cd₂Nb₂O₇ by substitution of Cd²⁺ by other divalent cations and of oxygen by sulfur. This study shows the existence of ferroelectric phases at room temperature when the oxygen ions in Cd₂Nb₂O₇ are partially replaced by sulfur ions. The ferroelectric behavior of CdZnNb₂O₆S above room temperature is reported.     

Synthesis, structure, UV-Vis-IR spectra, magnetism and theoretical studies on Cu[(2-aminomethyl)pyridine](thiocyanate)2 and comparisons with an analogous Cu complex

The title complex was synthesized under self-assembly conditions using Cu(acetate)₂·H₂O, 2-amp (= 2-aminomethylpyridine) and KSCN, and was characterized by IR, elemental analysis and single crystal structural analysis, and its spectral and RT magnetic properties were investigated. The asymmetric unit consists of a square planar Cu(II) center, with two ligand N atoms and two anionic Ns forming the square plane. In the unit cell, the monomeric complex assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu²⁺. Further, the structure was satisfactorily modeled by calculations based on Density Functional Theory (DFT), and the UV-Vis and IR spectra are analyzed in depth with the help of Time Dependent DFT (TDDFT). The results indicate that the absorption maxima are at relatively high energy and are mainly assigned to π → π^∗ transitions (in pyridine), with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d-d transition band. Also, it has been found that when the ligand ratio is modified, the formation of Cu(2-amp)₂(SCN)₂ takes place under the same self-assembly conditions, whose structure only has been recently reported. Structural, spectral and theoretical comparisons are presented for both complexes.     

Density Functional Theory Investigation of Structures and Electronic Spectra of N-protonated Corroles

The geometries and electronic spectra of a series of N-protonated corroles, including unsub-stituted H₄Cor⁺ and meso-triaryl substituted H₄TPC⁺, H₄TpFPC⁺, and H₄TdCPC⁺, were theoretically studied with density functional theory (DFT). The results indicate that all these compounds have two conformers, one with C₂ symmetry (denoted as S1) is more stable than the other (denoted as S2, C₁ symmetry) by 15.8?18.5 kJ/mol. The corrole macrocycles of these compounds show significant out-of-plane deformation. The enantiomerizations of the chiral S1 conformers were found to be a multi-step process with the S2 conformers as the in-termediates. Electronic absorption spectra and electronic circular dichroism (ECD) of these compounds were calculated with time-dependent DFT. In comparison with H₄Cor⁺, the UV-Vis absorptions of meso-triaryl species are significantly red-shifted and their Q bands are enhanced due to the π-π conjugation between the aryl and corrole rings. Several neighboring electronic transitions were calculated with opposite signs in rotatory strengths, suggesting that ECD spectroscopy may be a useful tool in studying the electronic transitions of these compounds.     

Effect of histidine on the sensitized generation of singlet oxygen in the complexes with chlorophyll

The energies of the intermolecular interactions of an O₂ molecule in the ground and excited states with the electron-excited and non-excited model complexes of chlorophyll were calculated using the DFT, CASSCF, SA-CASSCF, MCQDPT2, and XMCQDPT2 methods. The activation energies of formation and dissociation of the oxygen complexes were estimated. The radiative electric dipole moments of (0 → 0) spin-allowed S → S, T → T, and spin-forbidden S → T transitions were calculated taking into account the spin-orbit coupling, and rate constants of nonradiative transitions that determine the generation and deactivation of the O₂ molecule (¹Δ_g) were evaluated. The effect of histidine on the probability of singlet oxygen generation sensitized by the model chlorophyll complex was considered in detail.     

Neutron diffraction evidence for anion sublattice disordering in alkali earth fluorides at high temperatures

High temperature powder neutron diffraction studies of calcium, strontium and barium fluorides indicate that there are large thermal motions associated with the anions. This suggests that the anion sublattice in these compounds with the fluoride structure may disorder at temperatures below the melting points. In S:F₂ this disordering appears at about 1370 K and for BaF₂ at about 1300 K. This is in good agreement with transitions of 1440 K and 1240 K, predicted from thermodynamic data.