Kinetics of decomposition of the liquid phase of the ternary system LiOH-H2O2-H2O in the presence of the solid phase of Li2O2 · H2O

The kinetics of decomposition of hydrogen peroxide in the liquid phase of the ternary system LiOH-H₂O₂-H₂O was studied in the presence the solid phase of Li₂O₂·H₂O and without it. The main kinetic parameters of the processes studied were determined.     

Refining the Phase Diagram of the System 3Al2O3·2SiO2-ZrO2

The quasi-binary section mullite-zirconium dioxide in the ternary system Al₂O₃-SiO₂-ZrO₂, described by an eutectic phase diagram with T _{e u t} = 1750°C, was studied experimentally.     

Is the trinuclear complex the true reducing species in the Cp2TiCl2/Mn- and Cp2TiCl2/Zn-promoted pinacol coupling?

Through a combination of kinetic, voltammetric and product analysis, it has been found that a common Ti^III species obtained from the metal reduction of Cp₂TiCl₂ is involved in the electron transfer to benzaldehyde. A common species in the pinacol dimerization step was also demonstrated. In neither of the two steps is it necessary to invoke trinuclear complexes as previously proposed.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.     

Topology of the electron density of multicenter bonding in the anion TCNE2 2−

For TCNE₂ ^2? the role of bond paths in the electron density is emphasized to show that the anion contains multicenter bonding interactions across 4 central carbon atoms conferring inherent stability to it, consistent with experimental, and theoretical studies of other authors.     

Study of the system Pr2O3-SeO2-H2O at 100°C and the properties of the compounds obtained

The solubility of the system Pr₂O₃-SeO₂-H₂O at 100°C was studied. The fields of crystallization of Pr₂(SeO₃)₃·H₂O, PrH(SeO₃)₂, Pr(HSeO₃)₃ were established. The compounds obtained were identified by means of chemical, X-ray and thermal analysis. The thermal decomposition of Pr₂(SeO₃)₃·H₂O, PrH(SeO₃)₂, and Pr(HSeO₃)₃ was determined.This revised version was published online in November 2005 with corrections to the Cover Date.     

Study on the sulfinatodehalogenation of BrCF_2CF_2R

Sodium dithionite initiated sulfinatodehalogenation of BrCF2CF2R is studied.     

Theoretical studies on reactions of the stabilized H2COO with HO2 and the HO2···H2O complex

The reactions of H(2)COO with HO(2) and the HO(2)···H(2)O complex are studied by employing the high-level quantum chemical calculations with B3LYP and CCSD(T) theoretical methods, the conventional transition-state theory (CTST), and the Rice-Ramsperger-Kassel-Marcus (RRKM) with Eckart tunneling correction. The calculated results show that the proton transfer plus the addition reaction channel (TS1A) is preferable for the reaction of H(2)COO with HO(2) because the barriers are -10.8 and 1.6 kcal/mol relative to the free reactants and the prereactive complex, respectively, at the CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(d,p) level of theory. Furthermore, the rate constant via TS1A (2.23 × 10(-10) cm(3) molecule(-1) s(-1)) combined with the concentrations of the species in the atmosphere demonstrates that the HO(2) radical would be the dominant sink of H(2)COO in some areas, where the concentration of water is less than 10(17) molecules cm(-3). In addition, although the single water molecule would lower the activated barrier of TS1A from 1.0 to 0.1 kcal/mol with respect to the respective complexes, the rate constant is lower than that of the reaction of HO(2) with H(2)COO.     

Calculated vibrational structure of the first band of the photoelectron spectrum of HO 2 − and the electron affinity of HO2

The vibrational structure of the first band of the photoelectron (PE) spectrum of HO ₂ ^? and DO ₂ ^? has been calculated on the basis of (slightly modified) ab initio potentials. The best agreement with the experimental spectrum of HO ₂ ^? is obtained for a vibrational temperature of ca. 600 K. “Peak D”, which has been under debate in earlier work, is composed of two transitions, with the “hot” transition 3 ₁ ¹ being more intense than the adiabatic transition. Since thev ₂ bending mode of DO₂ has significant OO stretching character, the vibrational structure of the PE spectrum of DO ₂ ^? is more complex than that of HO ₂ ^? . Large-scale RCCSD(T) calculations of the equilibrium electron affinity of HO₂ yield 1.058 eV which agrees with the experimental value of 1.044 ± 0.020 eV.     

Density functional theory study of the styrylbenzoquinoline dyad and the related dibenzoquinolylcyclobutane formed in the [2 + 2] photocycloaddition reaction

The structure and electronic properties of the biphotochromic dyad with two styrylbenzo[f]quinoline photochromes, as well as the corresponding cyclobutane with two benzo[f]quinoline (BQ) substituents, are studied by DFT at the M06-2X/6-31G* level, the cyclobutane being a product of the [2 + 2] photocycloaddition (PCA) reaction of the dyad. According to calculations, the dyad forms π-stacked folded conformers, which, when excited, can form excimers that are precursors of cyclobutane. TD DFT calculations and natural transition orbital (NTO) analysis indicated that the lowest singlet excited S₁ state in the dyad is localized on the SBQ photochrome, including the ethylene group that undergoes PCA. Thus, the conditions for concerted electrocyclic reactions are satisfied, and the direct PCA follows the Woodward–Hoffmann rules. In contrast, in cyclobutane, the S₁ state is localized on the BQ substituent rather than on the cyclobutane core. Therefore, the reverse ring-opening (retro-PCA) reaction cannot follow the Woodward-Hoffmann rules and inevitably involves a step of excitation energy transfer from BQ to cyclobutane, which means the predissociation mechanism.     

Electronic structure of the doped SnO_2

SnO2 doped with La, Ce, Sm, Zn, Ca, Al and Sb was prepared by sol-gel technique and characterized by TEM, BET, XPS and XAES. The effect of the dopants on the grain sizes of SnO2 was described and especially the effect of dopants on the distribution of the electronic state density (DESD) of Sn4d orbital was studied deeply by using X-ray-induced Auger electron spectros-copy (XAES). It was observed that the dopants could influence not only the grain sizes of SnO2 but also electronic structure of SnO2, as well as the stability of the doped SnO2 samples. The experiment results indicated that the structure and stability of SnO2 film could be improved by the chemical modification of the dopants.     

Influence of NO on the Reduction of NO2 with CO over Pt/SiO2 in the Presence of O2

Reduction of NO2 with CO in the presence of NO and excess oxygen, a model mixture for flue gas, over a 0.1% Pt/SiO2 catalyst was studied. The related reaction mechanisms, such as oxidation of CO and NO, were discussed. It was found that there was a narrow temperature window （180-190 ℃） for the reduction of NO2 by CO. When the temperature was lower than the lower limit of the window, the reduction hardly occurred, while when the temperature was higher than the upper limit of the window, the direct oxidation of CO by O2 occurred and thereby NO2 could not be effectively reduced by CO. The presence of NO shifted the window to higher temperatures owing to the inhibition effect of NO on the activation of O2 on Pt, which made it possible to reduce NO2 by CO in flue gas.     

Quantum Topological Studies on the Molecular Complexes-CO_2-NCH and CO_2-OH_2

Topological properties of charge distribution for the title complexes and their constituent are analyzed by using ab initio calculations at 3-21G basis set. The results obtained are compared with those originated from ab initio and energy decomposition method. It has been determined that the title molecular complexes are T-shaped. The characteristics of the bonds and the changes originated from the formation of the complexes are discussed.     

Studies on the Reaction Mechanism of Br2 ＋ I2 = 2IBr

1 INTRODUCTION Interhalogen compounds have played an impor- tant role in environment and chemical engineering production. During the course of ozone exhaustion induced by sunlight in polar region, Br2, BrCl and HOBr are all precursors of Br atom[1]. Lately, scien- tists have detected that the content of BrCl in polar region sunlight was 35 ppt, larger than that of Br2 (25 ppt). Previous studies suggested that the con- centration of BrCl and O3 exhibits obvious negative correlation: w…     

Vibronic coupling in the A2Π and B2Σ+ electronic states of the NCS radical

The spin-rovibronic energy levels of the A(2)Π and B(2)Σ(+) electronic states of thiocyanate radical have been calculated variationally, using high-level ab initio coupled diabatic potential energy surfaces. Computations up to J = 7∕2 have been performed, obtaining all levels with K ≤ 3 (Σ(1/2),Π(1/2,3/2),Δ(3/2,5/2),Φ(5/2,7/2)), for energies up to 2000 cm(-1) above the A(000)(2)Π(3∕2) level. The available experimental data have been critically reviewed in the light of the theoretical findings.     

Theoretical Study on the Mechanism of VO2^＋ ＋ H2 Reaction in the Gas Phase

The mechanism of VO2+ + H2 reaction in the gas phase was investigated by using density functional theory (DFT) at the CCSD//B3LYP/6-311G(2d, p) level. According to our calculation results, the different reaction mechanisms were found for the singlet and triplet potential energy surfaces (PESs). Especially, the crossing points (CPs) among different PESs were located by means of the intrinsic reaction coordinate (IRC) approach presented by Yoshizawa et al., and the structures and energies of the corresponding minimum energy crossing points (MECPs) were obtained by the mathematical algorithm proposed by Harvey et al. Finally, the frontier molecular orbital (FMO) interaction analyses about MECP1 and MECP2 were used to prove our calculation results.     

An investigation of the polythermal diagram of the H2ONa2HPO4Na2SO4 system

The polythermal diagram of the ternary system H₂ONa₂HPO₄Na₂SO₄ has been established, setting up nine isotherms obtained between 0 and 25°C by conductimetric analysis. The solubility domains of the various solid phases have been determined. One eutectic, three stable and one metastable transitional transformations have been observed. Temperature and composition of the eutectic point have been obtained by thermal analysis at constant flow.     

Theoretical determination of the rate coefficient for the HO2 + HO2 → H2O2+O2 reaction: adiabatic treatment of anharmonic torsional effects

The HO(2) + HO(2) → H(2)O(2) + O(2) chemical reaction is studied using statistical rate theory in conjunction with high level ab initio electronic structure calculations. A new theoretical rate coefficient is generated that is appropriate for both high and low temperature regimes. The transition state region for the ground triplet potential energy surface is characterized using the CASPT2/CBS/aug-cc-pVTZ method with 14 active electrons and 10 active orbitals. The reaction is found to proceed through an intermediate complex bound by approximately 9.79 kcal/mol. There is no potential barrier in the entrance channel, although the free energy barrier was determined using a large Monte Carlo sampling of the HO(2) orientations. The inner (tight) transition state lies below the entrance threshold. It is found that this inner transition state exhibits two saddle points corresponding to torsional conformations of the complex. A unified treatment based on vibrational adiabatic theory is presented that permits the reaction to occur on an equal footing for any value of the torsional angle. The quantum tunneling is also reformulated based on this new approach. The rate coefficient obtained is in good agreement with low temperature experimental results but is significantly lower than the results of shock tube experiments for high temperatures.