氧原子与羟亚甲基自由基反应机理的理论研究

用量子化学从头计算法对氧原子与羟亚甲基自由基在最低双重态势能面上的反应进行了研究,计算了势能面上各驻点的构型参数、振动频率和能量。计算采用G2(MP2)理论方法。计算结果表明,反应首先形成中间体OCH_2OH,而后经不同过渡态解离为H_2CO+OH或H+HCOOH。由中间体形成甲醛和甲酸的过渡态的能量分别比反应物低202.5和355.3kJ/mol,计算得到2个反应通道的反应热分别为-314.1和-402.9kJ/mol,与实验结果(-307和-398kJ/mol)符合很好。根据能量数据可以预言形成甲酸的通道将是主要的反应通道。     

BF3活化高锰酸氧化丙烯酸反应机理的 密度泛函研究

用量子化学密度泛函理论(DFT)的B3LYP方法对高锰酸根离子与丙烯酸的环加成反应机理进行了系统研究, 全参数优化了反应势能面上各驻点的几何构型、振动频率和能量. 计算结果表明: 反应有两个竞争通道, 即[2+3]反应通道和[2+2]反应通道, 其中[2+3]通道比[2+2]通道的反应势垒降低了183.89 kJ/mol, 并通过在高锰酸根的氧原子上配位一个或两个BF3分子来研究BF3分子对反应体系的活化效应, 结合两个BF3分子使得[2+3]通道的反应势垒降低为23.97 kJ/mol, 则有利于反应按该通道进行, 然而[2+2]通道的反应势垒仍较高(>195 kJ/mol).这进一步表明该反应体系中加入一定量BF3能提高高锰酸氧化烯烃双键的化学活性.     

BF_3活化高锰酸氧化丙烯酸反应机理的密度泛函研究

用量子化学密度泛函理论(DFT)的B3LYP方法对高锰酸根离子与丙烯酸的环加成反应机理进行了系统研究,全参数优化了反应势能面上各驻点的几何构型、振动频率和能量.计算结果表明:反应有两个竞争通道,即[2+3]反应通道和[2+2]反应通道,其中[2+3]通道比[2+2]通道的反应势垒降低了183.89kJ/mol,并通过在高锰酸根的氧原子上配位一个或两个BF3分子来研究BF3分子对反应体系的活化效应,结合两个BF3分子使得[2+3]通道的反应势垒降低为23.97kJ/mol,则有利于反应按该通道进行,然而[2+2]通道的反应势垒仍较高(195kJ/mol).这进一步表明该反应体系中加入一定量BF3能提高高锰酸氧化烯烃双键的化学活性.     

二氟亚烷基卡宾与甲醛环加成反应机理的理论研究

用二阶微扰理论研究单重态二氟亚烷基卡宾与甲醛发生的环加成反应机理,采用MP2/6-31G^*方法计算了势能面上各驻点的构型参数、振动频率和能量.结果表明,单重态二氟亚烷基卡宾与甲醛的环加成反应主要有两种反应通道,通道1中,两个反应物经a,b和c三条反应途径生成三元环构型的产物P1,其中途径c是主反应途径,该途径有两步组成:(Ⅰ)二氟亚烷基卡宾与甲醛生成了1个富能中间体(INT1c),是无势垒放热反应,放出能量为219.18kJ/mol;(Ⅱ)中间体(INT1c)异构化为产物二氟亚烷基环氧乙烷,其势垒为134.71kJ/mol.通道2的反应途径由三步组成:(Ⅰ)反应物首先生成了1个富能中间体(INT1b),为无势垒的放热反应,放出的能量142.77kJ/mol;(Ⅱ)中间体(INT1b)异构化成另一中间体(INT2),其势垒为22.31kJ/mol;(Ⅲ)中间体(INT2)异构化成四元环构型产物P2,其势垒为11.98kJ/mol.     

气相中Cu+活化N2O中N-O键反应机理的理论研究

采用密度泛函UB3LYP/6 311+G(2d)方法计算研究了Cu+在基态和激发态下与N2O的反应机理,全参数优化了反应势能面上各驻点的几何构型,用频率分析方法和内禀反应坐标(IRC)方法对过渡态进行了验证,并用UCCSD(T)/6 311G(2d,p)、单点垂直激发、Harvey等人的方法分别进行各驻点单点能校正,单重态和三重态反应势能面交叉点CP确定,最低能量交叉点(MECP)的优化及MECP处相应的自旋 轨道耦合常数(SOC)计算。计算结果表明,该反应为一步反应,SOC值为84.2 cm-1,比较大的SOC值说明了在势能面上CP点处的翻转能够有效的降低反应的活化能,降低活化能值为27.6kJ.mol,增加反应放热126.7kJ.mol,这在动力学和热力学上对反应是非常有利。     

过渡金属离子与烷烃反应机理的理论研究: 镍离子与丙烷反应 中甲烷的还原消 除机理

用量子化学方法在B3LYP/6-311++g(3df,3pd)水平上研究了Ni^+与C3H8的反应,获得了[Ni,C3,H8]^+基态(双重态)势能面上CH4还原消除的详细机理。结果表明：该势能面上CH4消除反应经历两个基元步骤：Ni^+首先通过C—C活化过渡态形成插入型中间体,然后分别过不同的H-转移鞍点异构化为产物型中间体,并继而解离生成CH4,这些结果与以前从实验推测的反应机理明显不同。计算表明：对于该势面能上的甲烷消除反应,能量最有利的反应通道是Ni^+C3H8→Ni(C2H4)^++CH4,计算的反应热为127.85kJ/mol,与实验结果(106.13kJ/mol)符合较好。     

H2CO和NO2反应机理的密度泛函理论计算研究

用密度泛函理论方法在UB3LYP/ 6-311++G(d,p)并包含零点能水平上计算得到了H2CO和NO2反应的势能面.在势能面上找到了由H2CO和NO2反应生成HCO和trans-HONO的两条反应通道.直接H迁移反应通道的势垒只有90.54 kJ*mol-1,是主要的反应通道,其TST速率是7.9 cm3*mol-1*s-1,与文献值相符;另一条通道是H2CO异构化为trans-HCOH,然后C位H迁移,最后生成的HOC分子异构化为HCO,这条通道反应势垒高达348.03 kJ*mol-1,是一条次要反应通道.     

F+CH3OH碰撞反应机理和反应势能面

在MP2(full)/6-311++g(d,p)水平上详细研究了氟原子与甲醇抽氢反应的多通道反应机理,得到了各条通道中涉及的驻点的构型和振动频率及其能量,给出了两张完整的反应势能面.结果表明,氟原子从C原子上抽氢时有一条明显的最低能量通道,而从氧原子上抽氢时要涉及多条分支通道和多个驻点构型,给出了各分支通道的势能面示意图,结果表明以形成五元环状过渡态通道为优势通道.计算得到经途径1生成CH2OH时反应放热170.62kJ/mol,经分支途径6生成CH3O自由基时反应放热119.41 kJ/mol,此结果与实验值一致.     

CH3SH与H2O2气相反应机理的理论研究

采用密度泛函理论的B3LYP方法, 在6-311＋G(d,p)基组水平上研究了CH₃SH与H₂O₂的微观反应机理, 全参数优化了反应势能面上各驻点的几何构型, 振动分析和内禀反应坐标(IRC)分析结果证实了中间体和过渡态的真实性, 计算所得的键鞍点电荷密度的变化情况也确认了反应过程. 结果表明, 反应共分三大步进行, 包含两条反应通道, 第二步由IM1到CH₃SO₂H的反应为决速步骤, 其中的第一条通道是主要反应通道, 相应活化能为157.3和109.7 kJ/mol.     

F+CH_3OH碰撞反应机机理和反应势能面

以MP2（full）/6-311 + +g(d,p)水平上详细研究了氟原子与甲醇抽氢反应的 多通道反应机理，得到了各条通道中涉及的驻点的构型和振动频率及其能量，给出 了两张完整的反应势能面，结果表明，氟原子从C原子上抽氢时有一条明显的最低 能量通道，而从氧原子上抽氢时要涉及多条分支通道和多个驻点构型，给出了各分 支通道势能面示意图，结果表明以形成五元环状过渡态通道为优势通道，计算得到 经途径1生成CH_2OH时反应放热170.62kJ/mol，经分支途径6生成CH_3O自由基时反 应放热119.4 kJ/mol，此结果与实验值一致。     

Theoretical investigation of product channels in the CH3O2 + Br reaction

Several reaction pathways on the potential energy surface (PES) for the reaction of CH3O2 radicals with Br atoms are examined using both ab initio and density functional methods. Analysis of the PES suggests the presence of the stable intermediates CH3OOBr and CH3OBrO. CH3OOBr is calculated to be more stable than CH3OBrO by 9.7 kcal mol(-1) with a significant barrier preventing formation of CH3OBrO via isomerization of CH3OOBr. The relative importance of bi- and termolecular product channels resulting from the initially formed CH3OOBr adduct are assessed based on calculated barriers to the formation of CH2OO + HBr, CH3O + BrO, CH3Br + O2, and CH2O + HOBr.     

Disproportionation of Bromous Acid HOBrO by Direct O-Transfer and via Anhydrides O(BrO)(2) and BrO-BrO(2). An Ab Initio Study of the Mechanism of a Key Step of the Belousov-Zhabotinsky Oscillating Reaction

The results are reported of an ab initio study of the thermochemistry and of the kinetics of the HOBrO disproportionation reaction 2HOBrO (2) ? HOBr (1) + HBrO(3) (3), reaction ( R4' ), in gas phase (MP2(full)/6-311G*) and aqueous solution (SMD(MP2(full)/6-311G*)). The reaction energy of bromous acid disproportionation is discussed in the context of the coupled reaction system R2-R4 of the FKN mechanism of the Belousov-Zhabotinsky reaction and considering the acidities of HBr and HOBrO(2). The structures were determined of ten dimeric aggregates 4 of bromous acid, (HOBrO)(2), of eight mixed aggregates 5 formed between the products of disproportionation, (HOBr)(HOBrO(2)), and of four transition states structures 6 for disproportionation by direct O-transfer. It was found that the condensation of two HOBrO molecules provides facile access to bromous acid anhydride 7, O(BrO)(2). A discussion of the potential energy surface of Br(2)O(3) shows that O(BrO)(2) is prone to isomerization to the mixed anhydride 8, BrO-BrO(2), and to dissociation to 9, BrO, and 10, BrO(2), and their radical pair 11. Hence, three possible paths from O(BrO)(2) to the products of disproportionation, HOBr and HOBrO(2), are discussed: (1) hydrolysis of O(BrO)(2) along a path that differs from its formation, (2) isomerization of O(BrO)(2) to BrO-BrO(2) followed by hydrolysis, and (3) O(BrO)(2) dissociation to BrO and BrO(2) and their reactions with water. The results of the potential energy surface analysis show that the rate-limiting step in the disproportionation of HOBrO consists of the formation of the hydrate 12a of bromous acid anhydride 7 via transition state structure 14a. The computed activation free enthalpy ΔG(act)(SMD) = 13.6 kcal/mol for the process 2·2a → [14a](?) → 12a corresponds to the reaction rate constant k(4) = 667.5 M(-1) s(-1) and is in very good agreement with experimental measurements. The potential energy surface analysis further shows that anhydride 7 is kinetically and thermodynamically unstable with regard to hydrolysis to HOBr and HOBrO(2) via transition state structure 14b. The transition state structure 14b is much more stable than 14a, and, hence, the formation of the "symmetrical anhydride" from bromous acid becomes an irreversible reaction for all practical purposes because 7 will instead be hydrolyzed as a "mixed anhydride" to afford HOBr and HOBrO(2). The mixed anhydride 8, BrO-BrO(2), does not play a significant role in bromous acid disproportionation.     

CBr+O_2反应在二重态势能面上的机理研究(英文)

用UB3LYP/6-311++G(d,p)和QCISD(单点能)的方法考察了CBr+O2反应在二重态势能面上的反应机理。研究发现该反应在高温过程中重要,且有两个产物通道,它们分别是BrCO+O和Br+CO2,其中前者为优势通道。为了弄清溴原子取代对次甲基与氧气反应的机理的影响,我们对CBr+O2反应与CH+O2反应的相似性和差异也作了讨论。结果表明:两反应的第一步都是CX(X=H,Br)自由基与氧气反应生成链状过氧化物XCOO,且溴原子取代对反应的活性、产物通道的数量和产物的形成过程等都有影响。     

A direct dynamics trajectory study of F- + CH(3)OOH reactive collisions reveals a major non-IRC reaction path

A direct dynamics simulation at the B3LYP/6-311+G(d,p) level of theory was used to study the F- + CH3OOH reaction dynamics. The simulations are in excellent agreement with a previous experimental study (J. Am. Chem. Soc. 2002, 124, 3196). Two product channels, HF + CH2O + OH- and HF + CH3OO-, are observed. The former dominates and occurs via an ECO2 mechanism in which F- attacks the CH3- group, abstracting a proton. Concertedly, a carbon-oxygen double bond is formed and OH- is eliminated. Somewhat surprisingly this is not the reaction path, predicted by the intrinsic reaction coordinate (IRC), which leads to a deep potential energy minimum for the CH2(OH)2...F- complex followed by dissociation to HF + CH2(OH)O-. None of the direct dynamics trajectories followed this path, which has an energy release of -63 kcal/mol and is considerably more exothermic than the ECO2 path whose energy release is -27 kcal/mol. Other product channels not observed, and which have a lower energy than that for the ECO2 path, are F- + CO + H2 + H2O (-43 kcal/mol), F- + CH2O + H2O (-51 kcal/mol), and F- + CH2(OH)2 (-60 kcal/mol). Formation of the CH3OOH...F- complex, with randomization of its internal energy, is important, and this complex dissociates via the ECO2 mechanism. Trajectories which form HF + CH3OO- are nonstatistical events and, for the 4 ps direct dynamics simulation, are not mediated by the CH3OOH...F- complex. Dissociation of this complex to form HF + CH3OO- may occur on longer time scales.     

BrO与CH3SH反应机理的量子化学及拓扑研究

利用密度泛函和电子密度拓扑分析方法对BrO与CH₃SH反应的微观机理进行了理论研究. 在B3LYP/6-311G (d, p)水平上对反应势能面上的各驻点进行几何构型的全优化; 振动分析和IRC计算证实了中间体和过渡态的真实性和相互连接关系; 计算得到了各反应通道的活化能, 并进行了零点能校正. 计算结果表明: 该反应存在7个反应通道, 其中生成CH₃S＋HOBr和CH₃SO＋HBr的通道为主要反应通道. 通过对反应过程中部分驻点的电子密度拓扑分析, 首次发现了接近平面的四元环状过渡态, 从而拓展了原来对环状结构过渡态定义的适用范围.     

An ab initio correlated study of the potential energy surface for the HOBr.H2O complex

The potential energy surface (PES) for the HOBr.H(2)O complex has been investigated using second- and fourth-order M?ller-Plesset perturbation theory (MP2, MP4) and coupled cluster theory with single and doubles excitations (CCSD), and a perturbative approximation of triple excitations (CCSD-T), correlated ab initio levels of theory employing basis sets of triple zeta quality with polarization and diffuse functions up to the 6-311++G(3dp,3df ) standard Pople's basis set. Six stationary points being three minima, two first-order transition state (TS) structures and one second-order TS were located on the PES. The global minimum syn and the anti equilibrium structure are virtually degenerated [DeltaE(ele-nuc) approximately 0.3 kcal mol(-1), CCSD-T/6-311++G(3df,3pd) value], with the third minima being approximately 4 kcal mol(-1) away. IRC analysis was performed to confirm the correct connectivity of the two first-order TS structures. The CCSD-T/6-311++G(3df,3pd)//MP2/6-311G(d,p) barrier for the syn<-->anti interconversion is 0.3 kcal mol(-1), indicating that a mixture of the syn and anti forms of the HOBr.H(2)O complex is likely to exist.     

Ultracold collisions and reactions of vibrationally excited OH radicals with oxygen atoms

We report a quantum dynamics study of O + OH (v = 1, j = 0) collisions on its ground electronic state, employing two different potential energy surfaces: the DIMKP surface by Kendrick and Pack, and the XXZLG surface by Xu et al. A time-independent quantum mechanical method based on hyperspherical coordinates has been adopted for the dynamics calculations. Energy-dependent probabilities and rate coefficients are computed for the elastic, inelastic, and reactive channels over the collision energy range E(coll) = 10(-10)-0.35 eV, for J = 0 total angular momentum. Initial state-selected reaction rate coefficients are also calculated from the J = 0 reaction probabilities by applying a J-shifting approximation, for temperatures in the range T = 10(-6)-700 K. Our results show that the dynamics of the collisional process and its outcome are strongly influenced by long-range forces, and chemical reactivity is found to be sensitive to the choice of the potential energy surface. For O + OH (v = 1, j = 0) collisions at low temperatures, vibrational relaxation of OH competes with reactive scattering. Since long-range interactions can facilitate vibrational relaxation processes, we find that the DIMKP potential (which explicitly includes van der Waals dispersion terms) favours vibrational relaxation over chemical reaction at low temperatures. On the DIMKP potential in the ultracold regime, the reaction rate coefficient for O + OH (v = 1, j = 0) is found to be a factor of thirteen lower than that for O + OH (v = 0, j = 0). This significantly high reactivity of OH (v = 0, j = 0), compared to that of OH (v = 1, j = 0), is attributed to enhancement caused by the presence of a HO(2) quasibound state (scattering resonance) with energy near the O + OH (v = 0, j = 0) dissociation threshold. In contrast, the XXZLG potential does not contain explicit van der Waals terms, being just an extrapolation by a nearly constant function at large O-OH distances. Therefore, long-range potential couplings are absent in calculations using the XXZLG surface, which does not induce vibrational relaxation as efficiently as the DIMKP potential. The XXZLG potential leads to a slightly higher reactivity (a factor of 1.4 higher) for O + OH (v = 1, j = 0) compared to that for O + OH (v = 0, j = 0) at ultracold temperatures. Overall, both potential surfaces yield comparable values of reaction rate coefficients at low temperatures for the O + OH (v = 1, j = 0) reaction.     

Quantum Chemical Study on the Reaction Mechanism of OBrO Radical with OH Radical

The reaction mechanism of OBrO with OH has been studied using the B3LYP/6-311 G(d,p) and the high-level electron-correlation CCSD(T)/6-311 G(d,p) at single-point. The results show that the title reaction could probably proceed by four possible schemes, generating HOBr O2, HBr O3, BrO HO2 and HOBrO2 products, respectively. The main channel is the one to yield HOBr O2. The whole reaction involves the formation of three-membered, four-membered and five-membered rings, followed by the complicated processes of association,H-shift, Br-shift and dissociation. All routes are exothermic.     

Uncatalyzed reactions in the classical Belousov-Zhabotinsky system. I. Reactions of bromomalonic acid with acidic bromate and with HOBr

The uncatalyzed reactions of bromomalonic acid (BrMA) with acidic bromate and with hypobromous acid were studied in 1 M sulfuric acid, a usual medium for the oscillatory Belousov-Zhabotinsky (BZ) reaction, by following the rate of the carbon dioxide evolution associated with these reactions. In addition, the decarboxylation rate of dibromomalonic acid (Br2MA) was also measured to determine the first-order rate constant of its decomposition (4.65 x 10(-5) s(-1) in 1 M H2SO4). The dependence of that rate constant on the hydrogen ion concentration suggests a carbocation formation. A slow oligomerization of BrMA observed in sulfuric acid solutions is also rationalized as a carbocationic process. The initial rate of the BrMA-BrO3- reaction is a bilinear function of the BrMA and BrO3- concentrations with a second-order rate constant of 3.8 x 10(-4) M(-1) s(-1). When a great excess of BrO3- is applied, then BrMA is oxidized mostly to CO2. A reaction scheme compatible with the experimental finding is also given. On the other hand, when less BrO3- and more organic substrate - BrMA or malonic acid (MA)--is applied, then addition reactions of various carbocations with the enol form of the organic substrates should be taken into account in later stages of the reaction. It was discovered that HOBr, which brominates BrMA to Br2MA when BrMA is in excess, can also oxidize BrMA when HOBr is in excess. As Br2MA does not react with HOBr, it is assumed that the acyl hypobromite, formed in the first step of the HOBr and BrMA reaction, can react with an additional HOBr to give oxidation products. It was found that the initial rate of the reaction can be described by the following experimental rate law: k(BHOB)[BrMA]0[HOBr]0(2), where k(BHOB) = 5 M(-2) s(-1). A reaction scheme for the oxidation of BrMA by HOBr is given for conditions where HOBr is in excess. Model calculations illustrate qualitatively that the suggested reaction schemes are able to mimic the experiments. (More quantitative simulations are prevented by kinetic data missing for the various carbocation intermediates.) Finally, the effects of these newly observed reactions on oscillatory BZ systems are discussed briefly.     

Mechanism and Tafel lines of electro-oxidation of water to oxygen on RuO2(110)

How to efficiently oxidize H(2)O to O(2) (H(2)O → 1/2O(2) + 2H(+) + 2e(-)) is a great challenge for electrochemical/photo water splitting owing to the high overpotential and catalyst corrosion. Here extensive periodic first-principles calculations integrated with modified-Poisson-Boltzmann electrostatics are utilized to reveal the physical origin of the high overpotential of the electrocatalytic oxygen evolution reaction (OER) on RuO(2)(110). By determining the surface phase diagram, exploring the possible reaction channels, and computing the Tafel lines, we are able to elucidate some long-standing puzzles on the OER kinetics from the atomic level. We show that OER occurs directly on an O-terminated surface phase above 1.58 V vs NHE, but indirectly on a OH/O mixed phase below 1.58 V by converting first the OH/O mixed phase to the O-terminated phase locally. The rate-determining step of OER involves an unusual water oxidation reaction following a Eley-Rideal-like mechanism, where a water molecule from solution breaks its OH bond over surface Os with concurrent new O-OH bond formation. The free energy barrier is 0.74 eV at 1.58 V, and it decreases linearly with the increase of potential above 1.58 V (a slope of 0.56). In contrast, the traditionally regarded surface oxygen coupling reaction with a Langmuir-Hinshelwood mechanism is energetically less favored and its barrier is weakly affected by the potential. Fundamentally, we show that the empirical linear barrier~potential relation is caused by the linear structural response of the solvated transition state to the change of potential. Finally, the general strategy for finding better OER anode is also presented.