O~+ + H_2及其同位素取代反应的立体动力学研究

运用准经典轨线方法,基于RODRIGO势能面,对碰撞能为20kcal/mol时,O++H2及其同位素取代反应的立体动力学性质进行了理论研究,对k-j′两矢量相关和k-k′-j′三矢量相关的分布函数、极化微分反应截面,以及产物转动取向参数进行了详细的讨论.结果表明,O++H2→OH++H,O++DH→OD++H和O++TH→OT++H反应的立体动力学性质对体系的质量因数非常敏感.     

He+H+2及其同位素取代反应的立体动力学研究

运用准经典轨线方法,基于AQUILANTI势能面, 在碰撞能为145 kJ/mol时,对He+H⁺₂及其同位素取代反应的立体动力学性质进行了理论研究.对k-j′两矢量相关和k-k′-j′三矢量相关的分布函数,以及产物转动取向参数进行了详细的讨论.结果表明,He+HH⁺→HeH⁺+H,He+HD⁺→HeH⁺+ 关键词： 矢量相关 立体动力学 准经典轨线方法     

A quasi-classical trajectory study of the Cl + H<Subscript>2</Subscript> (D<Subscript>2</Subscript>) reaction on a new BW3 potential energy surface

Molecular reaction dynamics of Cl + H₂ (D₂) has been studied on the latest analytical potential energy surface called BW3 using the Monte Carlo quasi-classical trajectory method. Excitation functions, differential cross sections and angular distributions of HCl and DCl products have been calculated. The excitation functions of the Cl (²P_3/2) + n-H₂ and Cl(²P_3/2) + n-D₂ reactions are also studied. The results are compared with those of quasi-classical trajectory [M. Alagia et al.: Phys. Chem. Chem. Phys. 2 (2000); F. J. Aoiz et al.: J. Phys. Chem. 100 (1996)], quantum mechanical (QM) calculations [F. J. Aoiz et al.:J. Chem. Phys. 115 (2001)] and experimental data [S. H. Lee et al.: J. Chem. Phys. 110 (1999); F. Dong et al.: J. Chem. Phys. 115 (2001)]. Discussions are given to some new results.     

Analyses of the semi-classical wavepacket approach to chemical reactions: the F + H2 → HF + H reaction

Mixed quantum-classical calculations using propagation of 3D wavepackets in hyperspherical coordinates have been performed for the F + H₂ → HF + H reaction using two different potential energy surfaces. Vibrationally resolved cross-sections show good agreement with those obtained from accurate quantum mechanical calculations.     

Widths and shifts of some plasma-broadened oxygen and carbon multiplets

Profile measurements for some multiplets of neutral oxygen and carbon have been carried out in a wall-stabilized d.c. cascade arc. A 3.4 m Ebert spectrograph with a dispersion of 1.1 mm/Å was adapted to simultaneous photoelectric scanning of two sources and was used. Different gas mixtures (O₂ + H₂O, O₂ + He, CO₂ + Ar + H₂) were used for the production of plasmas. Arc currents between 25 and 100 A yielded temperatures between 10,200 and 13,570 K and electron densities from 3.17 to 7.84 x 10¹⁶cm^-3. Using the nonlinear least-squares method, theoretical profiles of different types were fitted to sets of experimental points, and broadening parameters of multiplet components were obtained for one multiplet of CI and four multiplets of OI in the visible spectral region. Our electron-impact half-widths and shifts are compared with theoretical values and other experimental data. Reasonable agreement between theoretical and experimental results are found for OI 3947 Å, OI 4368 Å, OI 5436 Å, and CI 5798 Å. For the multiplet OI 5330 Å, the available theoretical values differ considerably and the difference between experimentally determined and calculated shift is too large. Griem's theoretical half-width is close to the experimental value.     

A computational study (DFT,MP2, and GIAO‐DFT) of substituent effects on protonation regioselectivity in β,β‐disubstituted vinyldiazonium cations: formation of highly delocalized carbenium/diazonium dications

Protonation reactions were studied by quantum‐chemical theoretical methods (DFT and MP2) for a series of β,β‐disubstituted vinyldiazonium cations ( 1 ⁺ – 14 ⁺ ), bearing stabilizing electron‐releasing groups (H₃CO? , (H₃C)₂N? , H₃C? , (H₃C)₃Si? , as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at C_α, at the β‐substituent, and at N_β were considered. The energetically most favored pathway in all cases was C_α protonation, which formally corresponds to trapping of the mesomeric diazonium ylid. Based on the computed properties (optimized geometries, NPA‐charge densities, and multinuclear GIAO‐NMR chemical shifts), the resulting dications can best be viewed as carbenium/diazonium dications, in which the carbocation is further delocalized into the β‐substituent. For the α‐nitro derivative 15 , protonation of the nitro group was predicted to be the most favored reaction, while C_α‐ and N_β‐protonation resulted in the loss of the nitronium ion. Copyright © 2009 John Wiley & Sons, Ltd.     

液态甲烷的高温密度物态方程理论研究

 采用热力学统计理论研究了液态甲烷在高温高压下分子分解反应特点及该体系的物态方程。着重讨论了体系中CH₄-H₂分子间有效势对体系化学反应平衡及物态方程的影响,并根据实验Hugoniot点(p_H, V)优化确定出其exp-6势函数中的参数值。该势函数的排斥部分值比理想混合条件下Lorentz-Berthelot规则给出的势函数值低约50%,预示着高压下CH₄和H₂之间存在着某种亲合性。用该势函数计算得到的p-T线与现有的两个实验点符合很好。还讨论了CH₄-H₂之间的有效作用势参数对CH₄分子冲击离解度（x）的影响。     

Study of the Characteristics of Elementary Processes in a Chain Hydrogen Burning Reaction in Oxygen

The characteristics of possible chain explosive hydrogen burning reactions in an oxidizing medium are calculated on the potential energy surface. Specifically, reactions H₂ + O₂ → H₂O + O, H₂ + O₂ → HO₂ + H, and H₂ + O₂ → OH + OH are considered. Special attention is devoted to the production of a pair of fast highly reactive OH radicals. Because of the high activation threshold, this reaction is often excluded from the known kinetic scheme of hydrogen burning. However, a spread in estimates of kinetic characteristics and a disagreement between theoretical predictions with experimental results suggest that the kinetic scheme should be refined.     

Diffusionstheoretische Beschreibung der Dissoziation und des Ionenhaushaltes im schwachionisierten Säulenplasma der Wasserstoffentladung. I. Reaktionsmechanismen — Bilanzgleichungssystem und Lösungsmethode

After the discussion of the main reaction mechanisms as ionization, dissociation, dissociative recombination, ion-molecule-reactions and chemical reactions between neutral particles a system of balance equations for the ions H⁺, H₂⁺, H₃⁺, and H₅⁺, for the atoms, for the mixture of neutral particles, for charge neutrality and the discharge current is given in the framework of the diffusion theory. The numerical method for the solution of this system is explained. In the following parts of this paper detailed results of the numerical calculation will be dicussed in comparison with some experimental investigations.     

An exact quantum mechanical study of the isotopic collinear reactive systems H2 + Cl and D2 + Cl

An exact quantum mechanical study is performed on the collinear reactive systems H₂ + Cl and D₂ + Cl. Using a LEPS surface with a barrier height of 0·33 eV, the reactive transition probabilities were derived. Isotopic effects, threshold effects, effects of opening of new states and the influence of the initial state are considered to some extent.     

Synchrotron radiation VUV double photoionization of CHF2Cl

VUV double photoionization of CHF₂Cl in an energy region 32–40 eV was investigated with photoionization mass spectroscopy by using synchrotron radiation. The double ionization energy of CHF₂Cl and appearance energies for its main fragment dications (CHCl²⁺, CF₂²⁺ and CHFCl²⁺), were determined with photoionization efficiency spectroscopy for the first time. The single point energies of CHF₂Cl and its parent dication (CHF₂Cl²⁺) were calculated using Gaussian 03 program and density functional theory (DFT and B3LYP functional). The vertical double ionization energy of CHF₂Cl was predicted by using B3LYP method and empirical equation. According to our research results, the experimental double ionization energy of CHF₂Cl is in good agreement with the theoretically calculated vertical double ionization energy. The mechanism of double photoionization of CHF₂Cl was discussed based on the comparison of our experimental results with those predicted theoretically.     

From elementary reactions to evaluated chemical mechanisms for combustion models

Methods of determining rate data for elementary reactions for combustion applications, using experimental and theoretical methods, are briefly reviewed. The approaches are illustrated by reference to recent research in three areas: (i) reactions of OH with C₂H₄ and C₂H₂, where theory, tuned by reference to experiment, has provided a substantial contribution to the determination of rate data for these complex reactions, over a wide range of temperatures; (ii) reactions between alkyl radicals and O₂, where theory and experiment have been closely allied in discerning the details of mechanisms for small alkyl radicals; much remains to be done with larger radicals; (iii) reactions of methylene and the interactions between chemical reaction and the conversion of the singlet state into the triplet, where theory has played little part thus far. Comments are also made on the process of evaluating rate data for elementary reactions for incorporation in chemical mechanisms for use in combustion models.     

Thermal decomposition of dichloroketene and its reaction with H atoms

The thermal unimolecular decomposition of dichloroketene CCl₂CO → CCl₂ + CO (reaction 1) was studied experimentally and computationally. Dichloroketene was produced by the pulsed laser photolysis of hexachloroacetone, and the kinetics of its decay due to reaction 1 was monitored using photoionization mass spectrometry. Rate constants of reaction 1 were determined in direct time-resolved experiments as a function of temperature (740–870 K) and bath gas density ([He] = (3–25) × 10¹⁶ atom cm⁻³, [N₂] = 12 × 10¹⁶ molecule cm⁻³). Reaction 1 is in the falloff region under these conditions. The potential energy surface (PES) of reaction 1 was studied using quantum chemical methods. The experimental k₁ (T, P) dependence was reproduced with an RRKM/master equation model based on quantum chemical calculations. Parameterized expressions for the rate constants of reaction 1 and the reverse reaction, that of CCl₂ with CO, were obtained over wide ranges of temperatures and pressures. The enthalpy of formation of CCl₂CO was determined in quantum chemical calculations. The kinetics of the reaction of dichloroketene with hydrogen atoms (reaction 2), an important channel of destruction of CCl₂CO in flames, was studied computationally. The PES of reaction 2 was studied using quantum chemical methods. Temperature and pressure dependences of the rate constants of the four dominant reaction channels were obtained in transition state theory and master equation calculations; the technique of isodesmic reactions for transition states was applied to the channel of Cl atom abstraction. Analysis of the experimental data and the computational models of reactions 1 and 2 demonstrates that thermal decomposition is a major pathway of destruction for dichloroketene in combustion systems.     

A one-step procedure to prepare LiAsF6 and other allied lithium-based fluoro compounds used as electrolyte in lithium cells

A low-temperature all-solid-state thermal method has been developed to synthesize electrolytes like LiAsF₆, LiPF₆ and allied lithium-based fluoro-chemicals useful for lithium secondary cells. This developed procedure is simple and environmentally friendly compared with the existing procedures, which are poisonous and hazardous to health due to the use of obnoxious gases or liquids like F₂, AsF₃, PF₃, BF₃, AsF₃, or AsF₅, which are difficult to handle. In this proposed procedure, all chemicals are taken as analytical grade. Lithium salts and all other required salts are mixed well in required proportions and heated in between 300–400 °C to get the products examined by X-ray. The chemical reactions proposed for the preparation are given below.

1. 2LiOH + As₂O₅ + 12NH₄F → 2LiAsF₆ + 12NH₃ + 7H₂O
2. LiOH + (NH₄)₂HPO₄ + 6NH₄F → LiPF₆ + 8NH₃ + 5H₂O
3. 2LiOH + B₂O₃ + 8NH₄F → 2LiBF₄ + 8NH₃ + 5H₂O

     

Quantum chemical studies of the solvation of the hydroxide ion

Abstract

To understand and model the solvation of the hydroxide ion, OH(H₂O)^? _n clusters, n = 1?5, are studied using ab initio quantum chemical techniques, largely at the MP2 level of theory using a double zeta plus polarization functions basis extended by diffuse functions. Energies and vibrational frequencies, together with thermodynamic quantities such as enthalpies, entropies and Gibbs free energies, are computed. This permits comparison with experimental estimates of the successive thermodynamic changes associated with the reaction OH(H₂O)^? _n + H₂O → OH(H₂O)^? _n+1. The theoretical values are in good agreement with experiment. The free energy of hydration of OH^? is modelled by a composite discrete-continuum method where the effects of the first hydration shell (n = 3) are obtained from the gas phase cluster calculation, while the long-range effects are modelled using self consistent reaction field theory, namely by calculating the solvation energy of OH(H₂O)^? _n in a dielectric continuum. The best estimate of the solvation (free) energy at 298 K is ?84·5 kcal mol^?1, compared to the experimental value of ?102·8 kcal mol^?1.     

Zero-point energy,tunnelling, and vibrational adiabaticity in the Mu + H2 reaction

Isotopic substitution of muonium for hydrogen provides an unparalleled opportunity to deepen our understanding of quantum mass effects on chemical reactions. A recent topical review in this journal of the thermal and vibrationally state-selected reaction of Mu with H₂ raises a number of issues that are addressed here. We show that some earlier quantum mechanical calculations of the Mu + H₂ reaction, which are highlighted in this review, and which have been used to benchmark approximate methods, are in error by as much as 19% in the low-temperature limit. We demonstrate that an approximate treatment of the Born–Oppenheimer diagonal correction that was used in some recent studies is not valid for treating the vibrationally state-selected reaction. We also discuss why vibrationally adiabatic potentials that neglect bend zero-point energy are not a useful analytical tool for understanding reaction rates, and why vibrationally non-adiabatic transitions cannot be understood by considering tunnelling through vibrationally adiabatic potentials. Finally, we present calculations on a hierarchical family of potential energy surfaces to assess the sensitivity of rate constants to the quality of the potential surface.     

Synthesis and effect of Ce co-doping on photoluminescence characteristics of KZnSO4Cl: M (M=Dy or Mn) new phosphors

In the present paper KZnSO₄Cl:Ce³⁺, KZnSO₄Cl:Ce³⁺, Dy³⁺ and KZnSO₄Cl:Ce³⁺, Mn²⁺ new halosulfate phosphors were synthesized by wet chemical method. XRD and photoluminescence characterization of phosphors has been reported in this paper.     

Gas‐phase reactions of Cl atoms with hydrochloroethers: relative rate constants and their correlation with substituents' electronegativities

Rate constants for the reactions of Cl atoms with CH₃OCHCl₂ and CH₃OCH₂CH₂Cl were determined at (296 ± 2) K and atmospheric pressure using synthetic air as bath gas. Decay rates of these organic compounds were measured relative to the following reference compounds: CH₂ClCH₂Cl and n‐C₅H₁₂. Using rate constants of 1.33 × 10^?12 and 2.52 × 10^?10 cm³ molecule^?1 sec^?1 for the reaction of Cl atoms with CH₂ClCH₂Cl and n‐C₅H₁₂, respectively, the following rate coefficients were derived: k(Cl + CH₃OCHCl₂) = (1.05 ± 0.11) × 10^?12 and k(Cl + CH₃OCH₂CH₂Cl) = (1.14 ± 0.10) × 10^?10, in units of cm³ molecule^?1 s^?1. The rate constants obtained were compared with previous literature data and a correlation was found between the rate coefficients of some CH₃OCHR¹R² + Cl reactions and ΔElectronegativity of ? CHR¹R². Copyright © 2008 John Wiley & Sons, Ltd.     

H2F2 chain reaction rate investigation

Experimental performance of chemical lasers pumped by the H₂ + F₂ chain reaction has consistently fallen below expectations, although the “hot”, H+F₂→HF(ν)+F, pumping reaction produces greater vibrational excitation than the “cold”, F+H₂→HF(ν)+H, reaction used in most HF cw chemical lasers. The reasons for this discrepancy are examined by measuring spatially-resolved HF(ν) number density and the temperature profiles in a laminar, parallel flow, hydrogen-fluorine mixing layer and comparing the results with theoretical computations. By dissociating either the hydrogen or fluorine molecules with arc heaters, kinetics of the hot and cold reaction systems are separately investigated. From a comparison of the experimental vibrational populations and the theoretical predictions, it is concluded that: (1) previously-used pumping and deactivation rates associated with the cold reaction are approximately correct, (2) the deactivation of high vibrational levels populated by the hot reaction is much faster than previously stated in Ref. (1), and (3) the inclusion of multiquantum HF(ν) V-T (or V-R) deactivation reactions, which sharply decreases the number density of the upper vibrational levels, greatly improves the agreement between theory and experiment.