A priori rate constant for the reaction NH2+NO → N2+H2O

Capture rates for a dipole-dipole+Morse potential, from approximate semiclassical trajectory calculations, have been combined with RRKM rates for passing through entropy bottlenecks on the potential surface for NH₂ + NO → N₂ + H₂O. The resulting overall rate constants are in good agreement with experiment. The effective lifetime of the NH₂NO collision complex is found to be of the order of 10⁻¹¹s at room temperature, which accounts for the observed lack of pressure dependence of the rate constant. Calculated rate constants increase markedly at low temperatures, though not as rapidly as some of the experimental data would indicate.     

HNCO+OH-→NH2+CO2反应理论研究

用从头算UHF/6-31G基组研究了异氰酸和羟基生成氨基和二氧化碳即HNCO+OH→NH2+CO2的反应机理.优化得到了反应途径上的过渡态和中间体,并通过振动分析对过渡态和中间体进行了确认.在UMP4/6-31G水平上计算了它们的能量,同时对零点能进行了较正.计算结果表明:此反应是多步反应,先后通过3个过渡态(TS1,TS2,TS3),2个内旋转位垒(PSI,TSII),4个中间体(IM1,IM2,IM3,IM4),其中,IM3→TS2这一步为整个反应的决速步骤,速控步的活化能为202.388lJ/mol.与异氰酸和羟基作用的另一反应通道(即HNCO+OH→H2O+NCO)的活化能(69.038kJ/mol)比较,可看出所研究反应通道为次要反应通道,这与实验结果是一致的.     

Kinetics and dynamics of the NH3 + H → NH2 + H2 reaction using transition state methods, quasi-classical trajectories, and quantum-mechanical scattering

On a recent analytical potential energy surface developed by two of the authors, an exhaustive kinetics study, using variational transition state theory with multidimensional tunneling effect, and dynamics study, using both quasi-classical trajectory and full-dimensional quantum scattering methods, was carried out to understand the reactivity of the NH(3) + H → NH(2) + H(2) gas-phase reaction. Initial state-selected time-dependent wave packet calculations using a full-dimensional model were performed, where the total reaction probabilities were calculated for the initial ground vibrational state and for four excited vibrational states of ammonia. Thermal rate constants were calculated for the temperature range 200-2000 K using the three methods and compared with available experimental data. We found that (a) the total reaction probabilities are very small, (b) the symmetric and asymmetric N-H stretch excitations enhance the reactivity, (c) the quantum-mechanical calculated thermal rate constants are about one order of magnitude smaller than the transition state theory results, which reproduce the experimental evidence, and (d) quasi-classical trajectory calculations, which were performed with the main goal of analyzing the influence of the zero-point energy problem on the final dynamics results, reproduce the quantum scattering calculations on the same surface.     

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.     

H+HNCO→NH2+CO的反应机理及动态学计算

用从头算方法研究了H+HNCO→NH2+CO的反应机理: 首先经过H2NCO中间体,并为反应的控制步骤。在此基础上, 计算了控制步骤的反应途径, 沿反应途径的动态学性质和正则变分过渡态理论的速率常数。结果表明, 反应存在返回效应和隧道效应, 反应途径的曲率对隧道效应影响较大, 用变分过渡态方法和小曲率近似方法分别进行校正是有效的。     

NH4+-Mg2+-pO3-4-H+-H2O体系的优势区相图

通过优势区相图的构建对NH4+-Mg2+-PO43-H+-H2O体系的热力学平衡关系进行了研究.在不同镁、磷物质的量比和离子强度的条件下绘制了lgCT,Mg-lgC,T,P和lgCT,p-pH相图,确定了MgNH4PO4·6H2O、Mg3(PO4)2· 8H2O、MgHPO4· 3H2O和Mg(OH)2的热力学稳定区.结果表明,在相当广的pH范围内,MgNH4PO4·6H2O和Mg3(PO4)2·8H2O都是主要存在的固相;在较低pH和较高磷浓度的条件下,MgNH4PO4·6H2O和MgHPO4· 3H2O可以共存;而MgNH4PO4·6H2O和Mg(OH)2在碱性条件下更为稳定.当MgNH4PO4·6H2O、Mg3(PO4)2· 8H2O与液相共存、pH=9.08～9.52时,溶液总氮浓度达到最低值.lgCT,Mg-lgCT,P和lgCT,P-pH相图可以用于指导磷酸铵镁的沉淀-溶解平衡过程,有利于废水中氨氮的脱除和回收.     

Effects of NH 4 + and Cl− on the preparation of nanocrystalline TiO2 by hydrothermal method

Nanocrystalline TiO₂ powders with different morphologies and grain sizes were successfully synthesized by the hydrothermal method. Different concentrations of hydrochloric acid (HCl), ammonium chloride (NH₄Cl), ammonium sulfate [(NH₄)₂SO₄], and ammonium carbonate [(NH₄)₂CO₃] were used as additives in the hydrothermal process to investigate the effect of the concentration of ammonium (NH ₄ ⁺ ) and chloride ions (Cl^?) on the phase compositions, morphologies, and grain sizes of the prepared TiO₂. The as-synthesized samples were characterized by X-ray diffraction (XRD), transmission electron microscopy, Brunauer–Emmett–Teller analysis, and UV–Vis spectra. XRD results show that the as-synthesized powders are composed of anatase or a mixture of anatase and brookite. The grain size of the synthesized nano-TiO₂ powder ranged from 5.0 to 11.3 nm, and the related BET specific surface area varied from 127.5 to 191.0 m²/g. The photocatalytic activities of the prepared TiO₂ powders were evaluated by degradation of methylene blue (MB) in aqueous solution under UV light irradiation, and the results show that the photocatalytic performance of TiO₂ powders synthesized with additives is improved compared with that of TiO₂ prepared without any additives.     

N2S2 macrocyclic ligands. Synthesis and characterization of novel transition metal complexes of the type [LM(Si2Me6NH)2]2+ and [L′M(Si2Me6NH)2]2+

Summary Novel N₂S₂ macrocyclic ligands, L and L [SS-diethyl(1,3-diaminopropane) dithiocarbamate], [SS-cyclohexyl spiro-(1,3-diaminopropane) dithiocarbamate] and their complexes with Mn^II, Fe^II, Co^II, Ni^II and Cu^II have been characterized by elemental analyses, conductivity measurements, i.r., u.v.-vis. and n.m.r. spectra. The divalent transition metal complexes appear to be square planar and achieve octahedral geometry when treated with bis(trimethylsilyl)-amine to yield new heterobimetallic complexes.     

Is There an Entrance Complex for the F+NH3 Reaction?

Challenges associated with the theoretical and experimental kinetics of the F+NH₃→HF+NH₂ reaction suggest the need for a more‐precise potential surface. We have investigated the reactants and the products of the reaction, as well as the transition state and two complexes, with rather rigorous ab initio methods. The F????NH₃ complex existing in the entrance valley is predicted to lie 13.7 kcal mol^?1 below the reactants. A small classical barrier of 2.0 kcal mol^?1 separates this entrance well from products HF+NH₂. These results explain the observation by Persky of unprecedented inverse temperature dependence for the F+NH₃ rate constants. The strong hydrogen‐bonded complex FH????NH₂ exists in the exit valley, and with a binding energy of 9.9 kcal mol^?1 relative to separated products. The vibrational frequencies of all stationary points are predicted with the CCSD(T)/aug‐cc‐pVQZ method.     

Determination of the Rate Constants of the Reactions Cr + O2 + M → CrO2 + M and Cr + O2 → CrO + O

Kinetics and Catalysis - The rate constants of the interactions of chromium atoms with molecular oxygen through recombination Cr + O2 + M → CrO2 + M (I) and exchange Cr + O2 → CrO + O...     

H2O+KCl(饱和)+NaCl+NH4Cl的等压研究

Isopiestic measurements have been carried out at 298.15 K for the quaternary aqueous solution H2O+KCl(sat)+NaCl+NH4Cl saturated with potassium chloride and its ternary sub systems H2O+KCl (sat)+NaCl and H2O+KCl(sat)+NH4Cl. Taking sodium chloride (aq) or calcium chloride (aq) as reference solutions, osm otic coefficients and water activities of the aqueous solution were determined. The experiment results show that the isopiestic actions of the quaternary system related to its ternary sub-systems are in excellent agreement with the ideal like solution model.     

二维配位聚合物(NH3+CH2CH2NH3+)(NH2CH2CH2NH3+)2[(VO)4(PO4)4(H2O)2]·2H2O的水热合成及晶体结构

无机-有机杂化钒氧酸盐由于其结构的多样性以及在催化、医药、光、电、磁等材料领域中的应用前景而受到人们的广泛关注。近年来这一研究领域的重大进步是将有机氮配体或者过渡金属配合物直接连接到矾氧骨架上以获得各种新奇结构。合成出许多属于L/V/O、MXLY/V/O、L/P/V/O和MXLY     

Synthesis and Characterization of [NH3（CH2）2NH2（CH2）2NH3]BiCl6

1 INTRODUCTION During the past decade, a series of organic-inor- ganic hybrid compounds based on metal halide units have been prepared and studied[1]. The combination of organic and inorganic components at the mole- cular level affords us the opportunity to design new hybrid materials and modulate the properties of components[2]. As a result, some interesting proper- ties, such as non-linear optical[3], interesting magne- tic[4], efficient luminescence[2], ideal thermal and mechanical sta…     

H+、NH+4对HMX的N—NO2键解离能的影响

采用密度泛函理论的B3P86/6-31G**方法, 优化了β-HMX及其与H⁺、NH^+₄分别形成的复合物的稳定结构, 计算了β-HMX以及复合物中最弱的N—NO₂键解离能. 结果发现, HMX与H⁺、NH^+₄形成复合物后, 使HMX的构型产生较大变化; 与H⁺结合后, HMX的一个N—NO₂键显著伸长, 键级变小; 但与NH^+₄形成复合物后, HMX中键级最小的N—NO₂键长变化不大. 键解离能计算表明, 同β-HMX相比, 与H⁺形成的两种复合物中N—NO₂键解离能分别降低了近20 和82 kJ·mol^-1, 而HMX与NH^+₄形成的复合物中N—NO₂键解离能仅降低了约8 kJ·mol^-1, 表明H⁺对β-HMX的N—NO₂键的初始热裂解反应有促进作用, 而NH^+₄影响不明显.     

Theoretical Study on the Ion-pair Formation Mechanism for the Li + I2 → Li+ + I2- System

For the Li + I2 →Li+ + I2- system, theoretical study has been performed on the QCISD(T) level by using the ab initio method. The collision complex in ion-pair formation process was found and optimized. These results show that the crossed molecule beam (CMB) experimental phenomenon is verified and the detailed geometry is given for the first time. A mechanism for ion-pair formation was proposed in detail. The position where the collision complex occurs affects the reaction path. Specifically, the process has threshold when the collision complex appeared before the crossing point between the covalent and ionic state potential energy surfaces. On the contrary, the process has no threshold after the crossing point. Theoretically, the title system belongs to the former case.     

NH4+-TPA+-SiO2-Al2O3-H2O体系中ZSM-5沸石分子筛合成的研究

七十年代初期美国Mobil公司首先研究成功的ZSM-5沸石分子筛,由于它具有独特的孔道结构,对烷基化,异构化,选择裂化和甲醇合成汽油等反应具有独特的催化性能,目前已成为被普遍重视的新型催化剂材料^[1-4]。     

用变分过渡态理论研究NH_3+NH→2NH_2反应动力学

利用变分过渡态理论的“直接动力学”方法对ＮＨ３分子和基态ＮＨ（Ｘ３∑）自由基的反应进行了理论研究；利用从头算计算得到反应体系的电子结构能和能量梯度等信息，计算了２００～２５００Ｋ温度范围该反应的速率常数和穿透系数，分析了影响隧道效应和反应速率常数的一些因素．结果表明，在低温情况下，变分对于此反应影响较大，隧道效应特别明显．计算得到的速率常数和实验值符合得很好．     

生物铵转运蛋白对NH3/NH4+作用机理研究

铵转运蛋白广泛存在于细菌、真菌、植物以及动物等各种生命体中。生物铵转运蛋白对NH₃/NH₄⁺的传输作用已被广泛研究,然而,对于通过铵转运蛋白疏水性孔腔的物种是带电荷的NH₄⁺离子还是电中性的NH₃分子,仍存在很大争议。本文综述了近年来生物铵转运蛋白对NH₃/NH₄⁺作用机理的研究进展,主要包括NH₃或NH₄⁺的传输及NH₃和H⁺共传输等机理。     

RISM-SCF study of the free-energy profile of the Menshutkin-type reaction NH3+CH3Cl→NH3CH3++Cl− in aqueous solution

The free-energy profile for the Menshutkin-type reaction NH₃ + CH₃Cl → NH₃CH₃ ⁺ + Cl⁻ in aqueous solution is studied using the RISM-SCF method. The effect of electron correlation on the free-energy profile is estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have a large influence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies are utilized to calculate the zero-point energy correction of the free-energy profile. The computed barrier height and reaction exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms of the reaction are discussed from the view points of solute electronic and solvation structures. Received: 26 June 1998/Accepted: 28 August 1998 / Published online: 2 November 1998