Cluster bonding and energetics of the borane anions,BnHn2− (n = 5–12): A comparative study using bond length—bond enthal

Cluster bond enthalpies, E_L(BB), and orders, n?(BB), for the structurally characterised closo anions, B_nH_n^2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships E_L(BB) (kJ mol^?1) = 1.766 × 10¹¹ [L(BB)]^?4.0 and E_L(BB) (kJ mol^?1) = 318.8[n?(BB)]^0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, E_I, have been calculated using the relationships E_I(BB) = 297.9 I(BB) and E_I(BH) = 374.8I(BH) (enthalpies in kJ mol^?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of E_L and Σ E_L generally exceed those of E_I and Σ E_I by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of B_nH_n^2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ E_I values suggest that the anions are all of comparable stability, the ΣE_L values clearly show B₆H₆^2?, B₁₀H₁₀^2? and B₁₂H₁₂^2? to be more stable than B₈H₈^2?, B₉H₉^2? and B₁₁H₁₁^2?. The interatomic distances in B₇H₇^2? and in the unknown B₅ H₅^2? are estimated and used to assess their relative stabilities. The E_L values suggest that B₇ H₇^2? is of comparable stability to B₈H₈^2? etc., but show B₅H₅^2? as relatively unstable. The E_I values suggest that both of these anions should be relatively stable members of the series of closo anions.     

An extended Hückel study of hydrogen and oxygen chemisorption on Ru(001) surface

Extended Hückel MO theory has been applied to treat the chemisorption of hydrogen and oxygen atoms on Ru(001) surfaces. The site of chemisorption, surface-adatom distance, chemisorption energy and the vibrational frequency of the adatom on the surface have been calculated. For different sites, the chemisorption energy (E_c) results are as follows: For hydrogen, |E_c|(centre) > |E_c|(top) > |E_c|(bridge); while for oxygen, |E_c|(bridge) > |E_c|(top) > |E_c|(centre). These results are critically discussed in the light of the recent results obtained from the electron energy-loss spectroscopy (EELS) experiments.     

The influence of the conditions of the anodic formation and the thickness of Ag(I) oxide nanofilm on its semiconductor properties

The anodic formation of Ag(I) oxide nanofilms on polycrystalline silver and Ag–Au alloys as well as on low-index single crystals of silver in 0.1?М KOH was examined. By the methods of photocurrent i _ph and photopotential E _ph measurements, the n-type conductivity of Ag₂O film was established. Since the film (6–120 nm) is thinner than the space charge region, the dependence of photocurrent and photopotential appears on the film thickness L: i _ph ~L and E _ph ~L ². The transition from polycrystalline silver to single crystals as well as the addition of a small amount of gold (X _Au?≤?4 at.%) into the silver lattice decreases the degree of deviation from the stoichiometric composition Ag₂O. The parameters of Ag₂O film (optical absorption coefficient α, donor defects concentration N _D, space charge region W, and Debye’s length of screening L _D) depend on the index of a crystal face of silver, volume concentration of gold X _Au in the alloy, and film-formation potential E. At Е?=?0.52 V, the sequences of variation of these parameters correlate with the reticular density sequence. The growth of the potential disturbs these sequences. The band gap in Ag₂O formed on Ag_poly, Ag_hkl, and Ag–Au is 2.32, 2.23, and 2.19 eV. Flat band potential in Ag(I) oxide, formed on Ag_poly in 0.5 M KOH is 0.37 V. The appearance of the clear dependence between the state of the oxide/metal interface and the structure-sensitive parameters of semiconductor Ag(I) oxide phase allows considering the anodic formation of Ag₂O on Ag as a result of the primary direct electrochemical reaction, not of the precipitation from the near-electrode layer.     

Synthesis of B←N embedded indacenodithiophene chromophores and effects of bromine atoms on photophysical properties and energy levels

Developing novel fused π-conjugated chromophores has been an energetic research realm and knowing how to adjust their photophysical properties and energy levels through structure tailoring is of pivotal importance. Herein, based on the ladder-type π-conjugated indacenodithiophene (IDT) moiety, four B←N embedded IDT structures, namely, BNIDT, BNIDT-2Br, BNIDT-4Br, and BNIDT-6Br are synthesized and fully characterized. The influences of B←N unit embedded in the IDT backbone and Br atoms anchoring at the periphery on the photophysical properties and energy levels are discussed systematically. From IDT to BNIDT, a new intra-molecular charge transfer (ICT) transition band appears at lower energy (400–600?nm) in the absorption spectra with reduced optical bandgaps (E_g) from 3.25?eV to 2.11?eV and the fluorescence emission peaks red-shift from 390?nm to 565?nm along with remarkably extended fluorescence lifetimes from 1.2 ns to 12.4 ns due to the introduction of electron-deficient B←N into the backbone. Further anchoring Br atoms at the periphery of the backbone gives rise to depressed optical bandgaps, decreased fluorescence quantum yields (Φ), and shortened fluorescence lifetimes (τ) from BNIDT (E_g?=?2.11?eV, Φ?=?0.46, τ?=?12.4?ns), BNIDT-2Br (E_g?=?2.08?eV, Φ?=?0.18, τ?=?4.9?ns), BNIDT-4Br (E_g?=?1.67?eV, non-emission) to BNIDT-6Br (E_g?=?1.61?eV, non-emission). The HOMO and LUMO levels estimated from ultraviolet photoelectron spectroscopy (UPS) and optical bandgaps also experience synergetic lowering from IDT to BNIDT-6Br. This work indicates that backbone modification with electron-deficient B←N unit and side groups tailoring with halogen atoms are powerful to manipulate the optical properties and energy levels of fused π-conjugated chromophores.     

The electron correlation cusp

The Kais function is an exact solution of the Schrödinger equation for a pair of electrons trapped in a parabolic potential well with r ₁₂ ^?1 electron-electron interaction. Partial wave analysis (PWA) of the Kais function yields E _L = E + C₁(L + \-C ^?1 ₂)^?3 + O(L ^?5) where E is the exact energy and E _L the energy of a renormalized finite sum of partial waves omitting all waves with angular momentum ? > L. Slight rearrangement of an earlier result by Hill shows that the corresponding full CI energy differs from E _L only by terms of order O(L ^?5) with FCI values of C ₁ and \-C ^?1 ₂ identical to PWA values. The dimensionless \-C ₂ parameter is weakly dependent upon the size of the physical system. Its value is 0.788 for the Kais function, and 0.893 for the less diffuse helium atom, and approaches \-C ₂→ 1 in the limit of an infinitely compact charge distribution. The ?th energy increment satisfies an approximate virial theorem which becomes exact in the high ? limit. This analysis, formulated to facilitate use of the Maple system for symbolic computing, lays the mathematical ground work for subsequent studies of the electron correlation cusp problem. The direction of future papers in this series is outlined.     

A joint vibro-electronic mechanism in the dissociation of molecular hydrogen in nonequilibrium plasmas

A new mechanism Of H₂ dissociation in electrical discharges (10¹¹ ? n_e ? 10¹² cm^?3, 2.10^?16 ? E/N ? 3.10^?16 V cm², 300 ? T_g ? 1000 K, 3 ? p ? 30 torr) is presented and discussed. In this mechanism, called joint vibro-electronic mechanism (JVE), the electrons of the discharge create a strong vibrational disequilibrium with respect to the gas temperature (T_g) and promote electronic transitions from all vibrational levels of ¹Σ_g H₂ state to the repulsive ³Σ_u one. Moreover the V-V (vibration-vibration) and V-T (vibration-translation) energy exchanges are considered for building up the vibrational distribution of ¹Σ_g state. A complete set of e - D cross sections (e + H₂(¹Σ_g,ν) → e + H₂ (³Σ_u) → + 2H, ν = 0,14) is calculated by using an extension of the semiclassical Gryzinski theory in combination with the Franck-Condon principle. Dissociation rates calculated according to JVE are larger either than those obtained by the pure vibrational mechanism (PVM) discussed in our previous work or than those from the direct electronic impact mechanism (DEM) from the ground vibrational level. The behaviour of JVE rates as a function of gas temperature (T_g), of E/N, of electron density (n_e) and of pressure is then reported. The results show strong differences as compared, with the corresponding values obtained, with PVM. Finally the influence of the atoms as well as their recombination on the dissociation rates is discussed. The results have been obtained by solving a system of vibrational master equations.     

Kinetic description of bimolecular reactions with low energy cross sections in dilute gases

The rate ν of bimolecular chemical reaction A+A=B+C is analyzed for simple models of reactive cross sections. Collisions of particles colliding with energy E larger than a relatively low characteristic energy E _Lare either non-reactive (reversed Prigogine-Xhrouet model = rPX) or the ability to react is decreasing for E>E _L(reversed line-of-centres model = rLC). After solution of the Boltzmann equation analytical expressions for the distribution function f and the rate coefficient k have been derived. It is shown that the Arrhenius activation energy E _Ais small and even negative for sufficiently small E _L. The non-equilibrium corrections to ν are small.     

Influence of γ-radiation on the optical parameters of Ag10Te90 thin films

Amorphous Ag₁₀Te₉₀ thin films were prepared onto glass substrates using the thermal evaporation method. The effect of γ-irradiation on the optical parameters was investigated in the dose range 10–180 krad. The optical absorption coefficient (α) for the as-deposited and irradiated films has been determined from the reflectance (R) and transmittance (T) measurements in the wavelength range 400–900 nm. Analysis of the spectral behavior of the absorption coefficient in the absorption region revealed direct transitions. The optical studies showed the decrease in band gap (E_opt) with an increase in γ-irradiation . The width of the tails of localized states (E_e) were calculated and found to be increasing after γ-irradiation. Dielectric related optical constants, such as (n, k_ex., ε₁ and ε₂), were presented. Finally, the effect of γ-irradiation on the high-frequency dielectric constant (ε_L) and carrier concentration (N/m^*) is also studied. The results were discussed by the change on the degree of disorder as well as the radiation-induced effect on solids.     

Prediction of the terminations and Miller planes of the tetragonal zirconia thin films as a gate dielectric layer in integrated-circuit industry

In this paper, we investigate the structures and insulating characters of the tetragonal zirconia (t-ZrO₂) thin films with various possible terminations within the lower-index Miller planes (001) and (100). It is found that, firstly, a shift towards higher energy region makes the valence band of the OO-terminated thin films of the (001) Miller plane of t-ZrO₂ cross the Fermi level E_F and thus are unusable as a gate dielectric oxide in integrated-circuit (IC) industry because of large-leakage current. Secondly, a new splitting state presented just below the bottom of conduction band, and the Fermi level E_F drops between them, which imply that the Zr-terminated thin films of the (001) Miller plane of t-ZrO₂ are also unusable as a gate dielectric oxide in IC industry because of large leakage current. Thirdly, the insulating character disappears completely for Zr + OO-terminated thin films of the (001) Miller plane of t-ZrO₂ and thus is also unusable as a gate dielectric oxide in IC industry because of metal character. Fourthly, the insulating character is maintained for the ZrO₂-terminated thin films of the (100) Miller plane and thus is usable as a gate dielectric oxide in IC industry.     

Density functional study of H2 molecule and H atom adsorption on α‐U(001) surface

Density functional theory method has been employed to investigate the adsorption of H₂ molecule and H atom on α‐U(001) surface. There exist four initial sites [top (A), triangle‐center (B), long‐bridge (C), and short‐bridge (D)] for H₂ and H atom adsorptions on α‐U(001) surface. The E_ads (adsorption energy) values on the top sites of H₂‐U(001) configurations are around ?0.666 eV, and H₂ molecule has been elongated but not broken into H atoms. For the other three sites, the E_ads values are around ?1.521 eV. The long‐bridge site is the most reactive site for H₂ decomposing. For the H‐U(001) configurations, the E_ads are around ?2.904 eV. Top site and short‐bridge site are the most reactive sites for the H atom react on the α‐U(001) surface. Our work reveals that the different reactive sites play discrepant effects on hydrogenation process. Geometric deformations, diffusion paths, and partial density of states of H₂‐U(001) and H‐U(001) configurations have also been analyzed. Copyright © 2016 John Wiley & Sons, Ltd.     

The Liquid Junction Potential in Potentiometric Titrations. IX. The Calculation of Potentials Across Liquid Junctions of the Type, AY|AY+BY z(B)+HY+ A y L, for Emf Cells where Strong or Weak Complexes are Formed, Respectively, at [Y−] = C mol⋅L−1, Constant and −log 10[H+]≤ 7

In the present part, potential functions are derived for the calculation of the total potential anomalies, Δ E _B and Δ E _H, for Emf cells where strong or weak complexes are formed, respectively. A weak or strong electrolyte is considered to be used as complexing agent (A _y L), respectively, at the experimental condition, [Y^?] = C mol?L^?1, constant. The cells have indicator electrodes reversible to B ^z(B)+ (cell B) and H⁺ ions (cell H), respectively. The system, HY–BY _z(B)-A _Y L-AY and the protolysis of the acids HL and H₂L in the ionic medium (A⁺, Y^?) are studied. Here, y = |z _L |. Moreover, some useful Emf titrations are suggested for the experimental determination of the slope functions SL(H, L^?), SL (H, L^2?) and SL(H, HL^?). The usefulness of the derived potential functions is established using the H⁺-acetate^? (CH₃COO^?) system as an example.     

Ab-initio calculation of structural, electronic, and optical characterizations of the intermetallic trialuminides ScAl3 compound

We present first-principles study of the electronic and the optical properties for the intermetallic trialuminides ScAl₃ compound using the full-potential linear augmented plane wave method within density-functional theory. We have employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for calculating the electronic band structure and optical properties. The electronic specific heat coefficient (γ), which is a function of density of states, can be calculated from the density of states at Fermi energy N(E_F). The N(E_F) of the phase L1₂ is found to be lower than that of D0₂₂ structure which confirms the stability of L1₂ structure. We found that the dispersion of the band structure of D0₂₂ is denser than L1₂ phase. The linear optical properties were calculated. The evaluations are based on calculations of the energy band structure.     

Synthesis,characterization, magnetic,thermal and electrochemical studies of oxidovanadium (IV) picolyl hydrazones as functional catechol oxidase models

The picolyl hydrazone ligands derived from picolonic acid hydrazide and α-pyridyle ketone (L¹, L² and L³), α-acetyl thiophene (L⁴), α-formyl or α-acetyl phenol (L⁵ and L⁶ respectively) and 2-hydroxy-1-naphthaldehyde (L⁷) react with equimolecular amount of vanadyl sulfate in refluxing methanol to yield oxidovanadium (IV) complexes. The structure of the obtained ligands and their oxidovanadium (IV) complexes were characterized by various physicochemical techniques, viz. elemental analysis, molar conductance, magnetic susceptibility measurements, thermal analysis (TGA & DTG), IR, electronic absorption and ESR spectral studies. Cyclic voltammeteric behavior of the complexes has also been discussed. Five-coordinate square-pyramidal structure was proposed for all complexes. A monomeric nature was reported for complexes (2), (3), (6), and (7), while dimeric structures were suggested for complexes (1), (4) and (5). The ability of the complexes to catalyze the aerobic oxidation of catechol to the light absorbing o-quinone has been investigated. The results obtained show that all complexes catalyze this oxidation reaction and large variations in the rate were observed. Electrochemical data for most complexes show that there is a linear relationship between their ability to oxidize catechole and their E_1/2 potentials. The most effective catalysts were those complexes which exhibited E_1/2 values approached to the E° value of the natural tyrosinase enzyme isolated from mushroom, while those that largely deviated from that potential exhibited lower oxidase catalytic activity. The probable mechanistic implications of the catalytic oxidation reactions are discussed.     

Possibilities of applying the Piloyan method of determination of decomposition activation energies

Activation energies (E) of the thermal decomposition and the initial valuesT _D of the exotherms are determined for trinitroaniline, trinitro-m-phenylenediamine, trinitrotriaminobenzene, trinitrophenol, trinitroresorcinol, trinitro-m-cresol and hexanitrooxanilide. Linear relationships are derived between the termsE.T _D ^1? and published kinetics data on these compounds, obtained by an isothermal manometric method. The mechanisms of the primary steps in the thermolyses of these polynitro compounds are discussed. A positive influence on their thermal stability has been confirmed, arising from the contact of the measured compounds with the glass surface.     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

Use of electron-density contours from FSGO model wavefunctions: nonbonded radius of atoms and molecular anisotropy of the plarizability for some diatomic systems

Electron density contours (0.002 au) obtained from FSGO model wavefunctions are used to estimate “naturally partitioned” length (L_p) and width (W_p). The quantity L_p/W_p ? 1 is shown to be proportional to experimental molecular anisotropy (K) of polarizability. Predicted |K| values are used to estimate |α_| ? α| for a series of diatoms.     

Measurements ofL-subshell fluorescence yields for light and medium heavy elements (28≤Z≤47)

We report on the first determination ofL-subshell fluorescence yields, ω_Li, for various elements with 28≤Z≤47. The method applied is based on the subshell ionization by relativistic electron impact with an electron energy ofE ₀=50 keV and the detection of characteristic X rays by means of a high resolution crystal spectrometer calibrated absolutely with respect to its transmission and reflectivity. The number of initialL vacancies and its subshell distribution as well as the normalized X-ray transition probabilities, the Coster-Kronig yields and theK-shell Auger transition rates are taken from theory. The results obtained for ω_Li yield values that are for all three subshells in agreement with the predictions of a widely used semi-empirical formula and for ω _L2 and ω _L3 also with theoretical calculations. The values of ω _L1, however, exceed the theory systematically.     

Molecular dynamics study on the relationships of modeling, structural and energy properties with sensitivity for RDX-based PBXs

In this paper,a primary model is established for MD(molecular dynamics) simulation for the PBXs(polymer-bonded explosives) with RDX(cyclotrimethylene trinitramine) as base explosive and PS as polymer binder.A series of results from the MD simulation are compared between two PBX models,which are represented by PBX1 and PBX2,respectively,including one PS molecular chain having 46 repeating units and two PS molecular chains with each having 23 repeating units.It has been found that their structural,interaction energy and mechanical properties are basically consistent between the two models.A systematic MD study for the PBX2 is performed under NPT conditions at five different temperatures,i.e.,195 K,245 K,295 K,345 K,and 395 K.We have found that with the temperature increase,the maximum bond length(L max) of RDX N N trigger bond increases,and the interaction energy(E N-N) between two N atoms of the N-N trigger bond and the cohesive energy density(CED) decrease.These phenomena agree with the experimental fact that the PBX becomes more sensitive as the temperature increases.Therefore,we propose to use the maximum bond length L max of the trigger bond of the easily decomposed and exploded component and the interaction energy E N-N of the two relevant atoms as theoretical criteria to judge or predict the relative degree of heat and impact sensitivity for the energetic composites such as PBXs and solid propellants.     

Highly sensitive electrocatalytic determination of pyrazinamide using a modified poly(glycine) glassy carbon electrode by square-wave voltammetry

A new voltammetric sensor based on electropolymerization of glycine at glassy carbon electrode (GCE) was developed and applied to determine of pyrazinamide (PZA) by square-wave voltammetry (SWV). The initial cyclic voltammetric studies showed an electrocatalytic activity of poly(Gly)/GCE on redox system of pyrazinamide in 0.1 mol L^?1 phosphate buffer solution pH 7.5, with E _Pc and E _Pa in ?0.85 and ?0.8 V (versus E _Ag/AgCl), respectively. Studies at different scan rates suggest that the redox system of pyrazinamide at poly(Gly)/GCE is a process controlled by diffusion in the interval from 10 to 100 mV s^?1. Square-wave voltammetry-optimized conditions showed a linear response of PZA concentrations in the range from 0.47 to 6.15 μmol L^?1 (R?=?0.998) with a limit of detection (LOD) of 0.035 μmol L^?1 and a limit of quantification (LOQ) of 0.12 μmol L^?1. The developed SWV-poly(Gly)/GCE method provided a good intra-day (RSD?=?3.75 %) and inter-day repeatability (RSD?=?4.96 %) at 4.06 μmol L^?1 PZA (n?=?10). No interference of matrix of real samples was observed in the voltammetric response of PZA, and the method was considered to be highly selective for the compound. In the accuracy test, the recovery was found in the range of 98.2 and 104.0 % for human urine samples and pharmaceutical formulation (tablets). The PZA quantification results in pharmaceutical tablets obtained by the proposed SWV-poly(Gly)/GCE method were comparable to those found by official analytical protocols.     

Relation between the N-NO2 bond length and stability of the secondary nitramines

The fact of the constancy of activation entropy of N-NO₂ bond homolysis in a series of secondary nitramines was utilized for correction of the experimental values of activation energy E of this process proceeding from the reliable data for the rate constants of the nitramines decomposition in solutions. When comparing the refined values of E (kJ mol^?1) with the N-N bond length d _N-N (Å) the following correlations were obtained: for cyclic and framework nitramines E = 663 ? 356d _N-N, and for the aromatic nitramines E = 1810 ? 1227d _N-N. A linear relationship between E and d is observed in the series of similar compounds. It depends on the electronic and steric effects of substituents.