Ten-Dimensional Quantum Dynamics Study of H+CH3D→H2+CH2D Reaction

The mode selectivity of the H+CH3D→H2+CH2D reaction was studied using a recently developed ten-dimensional time-dependent wave packet method.The reac-tion dynam...     

Adiabatic and non-adiabatic quantum dynamics calculation of O(1D) + D2 → OD + D reaction

Adiabatic (1A' or 1A' state) and non-adiabatic (2A'/1A' states) quantum dynamics calculations have been carried out for the title reaction (O((1)D) + D(2) → OD + D) to obtain the initial state-specified (v(i) = 0, j(i) = 0) integral cross section and rate constant using the potential energy surfaces of Dobbyn and Knowles. A total of 50 partial wave contributions have been calculated using the Chebyshev wave packet method with full Coriolis coupling to achieve convergence up to the collision energy of 0.28 eV. The total integral cross section and rate constant are in excellent agreement with experimental as well as quasi-classical trajectory results. Contributions from the adiabatic pathway of the 1A' state and the non-adiabatic pathway of the 2A'/1A' states, increase significantly with the collision energy. Compared to the O((1)D) + H(2) system, the kinetic isotope effect (k(D)/k(H)) is found to be nearly temperature independent above 100 K and its value of 0.77 ± 0.01 shows excellent agreement with the experimental result of 0.81.     

Quantum-mechanical calculation of the reactions D + FH(ν = 0, 1, 2) → DF(ν′) + H and H + FD(ν = 0, 1, 2, 3) → HF(ν′) + D on a realistic potential energy surface

Collinear (two-mathematical-dimensional (2MD)) coupled-channel quantum-mechanical calculations have been performed on the reactions D + FH(ν = 0, 1, 2) → DF(ν′) + H and H + FD(ν = 0, 1, 2, 3) → HF(ν′) + D on a potential energy surface with a 40 kcal/mole barrier to exchange. This barrier height is close to that predicted by ab initio calculations and suggested by experiments. The relative effectiveness of reagent vibrational and translational excitation to promote reaction is considered. A one-mathematical-dimensional (1MD) model for these reactions is constructed and is shown to work very well for the D + FH reaction at high temperatures, and less well for that reaction at lower temperatures as well as for the reverse H + FD reaction. Possible reasons for the breakdowns of this model are discussed.     

Mean potential statistical theory of the H+ + D2 → HD + D+ reaction

The reactive collision process H(+) + D(2)(ν = 0, j = 0) → HD + D(+) is theoretically analyzed for collision energies ranging from threshold up to 1.3 eV. It is assumed that the reaction takes place via formation of a collision complex. In calculations, a statistical theory is used, based on a mean isotropic potential deduced from a full potential energy surface. Calculated integral cross sections, opacity functions, and rotational distributions of the HD products are compared with recent statistical and quantum mechanical calculations performed using a full potential energy surface. Satisfactory agreement between the results obtained using the two statistical methods is found, both of which however overestimate the existing quantum mechanical predictions. The effects due to the presence of identical particles are also discussed.     

A self-catenated network containing unprecedented 0D + 2D → 2D polycatenation array

Herein, we report a new acylamide ligand and its application in the construction of a metal-organic framework. The resultant acylamide metal-organic framework, namely [Zn(2)(L)(OH)(btc)](n) (1, L = N(1),N(4)-bis(pyridin-3-ylmethyl) naphthalene-1,4-dicarboxamide, H(3)btc = benzene-1,3,5-tricarboxylic acid), was obtained by hydrothermal synthesis. The outstanding structural feature of it is the 0D + 2D → 2D polycatenation array containing a self-catenated feature which has never previously been observed. To the best of our knowledge, the coexistence of self-catenation and polycatenation phenomena is highly exceptional.     

Infinite order sudden approximation treatment of the H + D2 → HD + D reaction

Results of a study of the H + D₂ → HD + D reaction within the quantum infinite order sudden approximation (RIOS) are reported here for the total energy range 1.0317 ⩽ E_t ⩽ 2.1417 eV. We present the vibrationally selected integral and total integral cross sections, and the latter are compared with both classical and experimental results. The RIOS results are in excellent agreement with the experimental results at 1.0317 eV and in reasonable agreement (≈ 20% high) at 2.1417 eV.     

Energy partitioning in O(1D2) reactions. I. O(D1D2) + H2S → OH(ν′) + HS

The complete vibrational distribution in the OH product of the reaction between O(¹D₂) and H₂S has been measured directly by the use of infrared emission spectroscopy under conditions appropriate to the stratospheric ozone layer. All energetically accessible vibrational levels are populated by the reaction. The vibrational distribution is inverted, having its maximum at OH(ν′ = 2 or 3). The reaction populating OH(ν′⩾1) partitions ≈ 44% of the available energy into OH vibration.     

Dynamic aspects of the reaction O(1D) + H2S → OH + SH

The energy distribution of nascent OH(²Π, υ, J) produced in the reaction of O(¹D) with H₂S has been measured by laser-induced fluorescence. The rotational distributions in υ″ = 0 and υ″ = 1 are Boltzmannian with temperature parameters T_r″-0 = 2300 ± 100 K and T_r⁻-1 = 2650 ± 150 K. A population ratio N(υ″ = 1)/N(υ″ = 0) = 0.17 is observed. The product-state distribution over the different spin and A components is statistically within the experimental uncertainty of 20%. A comparison of the OH product populations from the title reaction with the well known OH yield from the O(¹D)+H₂O reaction shows that 25% of the reactive encounters follow the reaction channel which produces OH in υ″ = 0 and υ″ = 1.     

Quasi-classical trajectory-gaussian binning study of the OH + D2 → HOD(v1',v2',v3') + D angle-velocity and vibrational distributions at a collision energy of 0.28 eV

The angle-velocity and product vibrational state distributions for the OH + D(2) reaction at a collision energy of 0.28 eV have been calculated using the quasi-classical trajectory-gaussian binning (QCT-GB) method and the Wu-Schatz-Lendvay-Fang-Harding (WSLFH) analytical potential energy surface. Comparison with high resolution molecular beam experiments shows that, differing from what happens when using the standard QCT method (i.e., histogram binning), very good results are obtained for both distributions. Hence, the strong differences previously observed between QCT and experimental results mainly come from an inadequate pseudoquantization of HOD rather than from other quantum effects. This is probably the first time that such a high level of agreement between theory and high resolution experimental data has been found in polyatomic reaction dynamics.     

17O excess transfer during the NO2 + O3 → NO3 + O2 reaction

The ozone molecule possesses a unique and distinctive (17)O excess (Δ(17)O), which can be transferred to some of the atmospheric molecules via oxidation. This isotopic signal can be used to trace oxidation reactions in the atmosphere. However, such an approach depends on a robust and quantitative understanding of the oxygen transfer mechanism, which is currently lacking for the gas-phase NO(2) + O(3) reaction, an important step in the nocturnal production of atmospheric nitrate. In the present study, the transfer of Δ(17)O from ozone to nitrate radical (NO(3)) during the gas-phase NO(2) + O(3) → NO(3) + O(2) reaction was investigated in a series of laboratory experiments. The isotopic composition (δ(17)O, δ(18)O) of the bulk ozone and the oxygen gas produced in the reaction was determined via isotope ratio mass spectrometry. The Δ(17)O transfer function for the NO(2) + O(3) reaction was determined to be: Δ(17)O(O(3)?) = (1.23 ± 0.19) × Δ(17)O(O(3))(bulk) + (9.02 ± 0.99). The intramolecular oxygen isotope distribution of ozone was evaluated and results suggest that the excess enrichment resides predominantly on the terminal oxygen atoms of ozone. The results obtained in this study will be useful in the interpretation of high Δ(17)O values measured for atmospheric nitrate, thus leading to a better understanding of the natural cycling of atmospheric reactive nitrogen.     

Third-body-assisted,binary ion—molecule reactions. The reaction NH+3 + H2 → NH+4 + H

The reaction NH⁺₃ + H₂ → NH⁺₄ + H was studied, in a selected-ion drift tube as a function of gas density and temperature from 20 to 298 K. A pressure dependence of the second-order rate coefficient was observed which indicates that the reaction rate is increased when the intermediate complexes collide with a third body. It is concluded that one has to be aware in general that a reaction that is found to be slow at low or moderate density can be significantly faster in a high-pressure environment.     

Crystallographic study of YCo3+1−2xCo2+xPt4+xO3 and DyCo3+1−2xCo2+xPt4+xO3

The crystal structures of single crystals of YCo³⁺_.36Co²⁺_.32Pt⁴⁺_.32O₃ and DyCo³⁺_.36Co²⁺_.32Pt⁴⁺_.32O₃ have been examined at room temperature, and shown to be isostructural with GdFeO₃, which belongs to space group Pbnm. The overall expansion of octahedra caused by substitution of platinum enhances the distortion of rare-earth dodecahedra by moving 4 out of 12 oxygens further away from the rare-earth ions, as shown by the rotation of octahedra along the [110] axis. No order has been found for Co²⁺, Co³⁺, and Pt⁴⁺.     

Capture and dissociation in the complex-forming CH(v = 0,1) + D2 → CHD + D, CD2 + H, CD + HD reactions and comparison with CH(v = 0,1) + H2

Rate coefficients for the CH(v = 0,1) + D(2) reaction have been determined for all possible channels (T: 200-1200 K), using the quasiclassical trajectory method and a suitable treatment of the zero point energy. Calculations have also been performed on the CH(v = 1) + H(2) reaction and the CH(v = 1) + D(2) → CH(v = 0) + D(2) process. Most of the results can be understood considering the key role played by the deep minimum of the potential energy surface (PES), the barrierless character of the PES, the energy of the reaction channels, and the kinematics. The good agreement found between theory and experiment for the rate coefficients of the capture process of CH(v = 0) + D(2), the total reactivity of CH(v = 1) + D(2), H(2), as well as the good agreement observed for the related CH(v = 0) + H(2) system (capture and abstraction), gives confidence on the theoretical rate coefficients obtained for the capture processes of CH(v = 1) + D(2), H(2), the individual reactive processes of CH(v = 1) + D(2), H(2), the abstraction and abstraction-exchange reactions for CH(v = 0) + D(2), and the inelastic process mentioned above, for which there are no experimental data available, and that can be useful in combustion chemistry and astrochemistry.     

Temperature dependence of the reaction NO + NO3 → 2NO2

The flash photolysis-visible absorption technique has been used to measure rate constants for the reaction NO + NO₃ → 2NO₂ (1) over the temperature range 224–328 K. The temperature dependence of the rate constant is given by the expression k₁(T) = (1.59 ± 0.32) × 10⁻¹¹exp(122/T) cm³ molecule⁻¹ s⁻¹ where the stated uncertainties refer to the ± 2σ limits from both random and systematic errors.     

NH+O3→ONH+O2反应热力学和动力学研究

在量子化学对 NH自由基与臭氧 O3反应计算的基础上,应用统计热力学方法研究了 100～ 1600 K温度范围内 NH和 O3反应过程的各热力学量的变化及平衡常数,用经 Wigner校正的 Eyring过渡态理论计算了不同温度下该反应两不同反应通道的活化热力学量、反应速率常数及频率因子.计算表明,相对于反应通道 II,反应通道 I不仅有很强的反应自发性,而且在动力学上也是较容易实现的反应.     

The reaction Ne+H 2 + (v=0, 1, 2, 3, 4)→NeH++H: 3D potential energy surface and quasiclassical trajectory calculations

A three-dimensional potential energy surface for the endoergic reaction Ne+H ₂ ⁺ →NeH⁺+H in the² A′ ground state of the system NeH ₂ ⁺ has been calculated by quantum chemical ab initio methods (CEPA approximation). The calculated points on this surface were fitted to an analytic ansatz in terms of an extended LEPS functional form augmented by a correction function. The latter was expanded in polynomials in inverse powers of the internuclear distances. This analytic form was used for quasiclassical trajectory calculations of reactive cross sections. In agreement with experimental investigations a strong vibrational enhancement is observed, i.e. the reaction is markedly favored if the necessary reaction energy is supplied as vibrational energy of H ₂ ⁺ rather than as relative translational energy. Other properties of the reaction dynamics such as the backward to forward scattering ratio, the lifetime of the collision complex NeH ₂ ⁺ , and final rotational and vibrational state distributions are also discussed on the basis of the quasiclassical trajectory calculations.     

Differential cross sections for H + D2 → HD(v' = 2, j' = 0,3,6,9) + D at center-of-mass collision energies of 1.25, 1.61, and 1.97 eV

We have measured differential cross sections (DCSs) for the reaction H + D(2) → HD(v' = 2,j' = 0,3,6,9) + D at center-of-mass collision energies E(coll) of 1.25, 1.61, and 1.97 eV using the photoloc technique. The DCSs show a strong dependence on the product rotational quantum number. For the HD(v' = 2,j' = 0) product, the DCS is bimodal but becomes oscillatory as the collision energy is increased. For the other product states, they are dominated by a single peak, which shifts from back to sideward scattering as j' increases, and they are in general less sensitive to changes in the collision energy. The experimental results are compared to quantum mechanical calculations and show good, but not fully quantitative agreement.     

The H + D2 → HD + D reaction at 0.55, 0.98, 1.10 and 1.30 eV: A distorted-wave study using a new distortion potential

The static-static distorted-wave method has been applied to the H+D₂(v = 0, j = 0) → HD(v', j')+D reaction on the LSTH potential energy surface at four energies. A new static distortion potential has been used that is obtained from the preferred collinear configuration of the atoms together with an average over the unperturbed molecular wavefunction. The rotational distributions agree well with recent experimental data and with other theoretical information.     

Synthesis of Epoxyalkyl (1→3)‐β‐D‐Oligoglucosides

Abstract

We describe an approach for the synthesis of (1→3)‐β‐D‐oligosaccharide derivatives 10–18. 1–9 were synthesized by treating peracetylated (1→3)‐β‐D‐oligosaccharides with the corresponding alkenyl alcohols and Lewis acid (SnCl₄) catalyst. Epoxidation of the corresponding alkenyl oligoglucosides took place by m‐CPBA. NaOMe in dry methanol was used for the deacetylation of the blocked derivatives, to give 10–18 in overall yields of 25–32%.