噻吩光解反应机理的理论研究

使用密度泛函理论(DFT)中的B3LYP方法, 采用6-31G**和6-31＋＋G**基组, 对噻吩的光解反应进行了理论研究. 对照实验结果, 我们研究了五个光解通道, 包括生成C₄H₄＋S, C₂H₂＋C₂H₂S和CS＋C₃H₄的三个闭壳层分子解离通道与生成HCS＋C₃H₃和HS＋C₄H₃的自由基解离通道. 各个可能的反应通道的产物碎片的具体形式得到了确认. 研究发现在基态生成C₂H₂＋C₂H₂S和在最低三态生成C₄H₄＋S的反应从能量上考虑最为有利, 而实验上观测到的主要产物C₂H₂＋C₂H₂S主要是在基态上产生的. 通过对比实验结果与计算结果, 我们认为噻吩光解反应机理与所用激发光波长有关.     

氟氯酰与丙烷反应的密度泛函理论研究

应用密度泛函理论(DFT), 对氟氯酰(ClF₃O)引发丙烷(C₃H₈)反应生成C₃H₇自由基或丙醇等产物的机理进行了研究. 在B3PW91/6-311＋＋G(d,p)水平上优化了9个不同反应通道上各驻点物(反应物、中间体、过渡态和产物)的几何构型, 并计算了它们的振动频率和零点振动能. 通过零点能校正计算了各反应路径的活化能, 并应用过渡态理论计算了各反应路径常温下的速率常数k. 计算结果表明: ClF₃O与C₃H₈反应可经过不同路径生成HF, C₃H₇自由基和C1F₂O自由基或C₃H₇OH和ClF₃. 其中, 最可几反应路径为ClF₃O分子的中间位F原子进攻丙烷β位H原子的反应, 活化能仅为7.54 kJ/mol, 速率常数为0.153×10⁶ mol^－1•dm³•s^－1.     

Al+与乙硫醇团簇的气相化学反应的实验和理论研究

利用激光溅射-分子束的方法研究了Al⁺和乙硫醇的气相化学反应,结果观察到了Al⁺与1～6个乙硫醇分子形成的团簇离子. 对团簇离子进行了密度泛函理论计算,找到了两种类型的异构体Al⁺(C₂H₅SH)_n和HAl⁺SC₂H₅(C₂H₅SH)_n-1,计算得到了相应的稳定结构和能量.分析质谱信号强度,结合理论计算结果,可推测出实验得到的n=1的产物离子是Al⁺(C₂H₅SH). n=2和3时产物离子开始转变为HAl⁺SC₂H₅(C₂H₅SH)_n-1, n=4时,HAl⁺SC₂H₅(C₂H₅SH)₃和Al⁺(C₂H₅SH)₄两种产物离子都存在,n≥5以后,团簇离子Al⁺(C₂H₅SH)_n开始成为主要的产物离子.     

激光诱导的亚硝酸与二苯醚的反应机理

355 nm光照下利用瞬态吸收光谱技术进行了有氧、无氧条件下二苯醚与亚硝酸体系的反应机理研究, 考察了其中瞬态物种的衰减行为, 并对其光解产物进行了GC-MS分析. 研究表明, HNO₂在355 nm紫外光的照射下产生的OH自由基和二苯醚反应生成C₁₂H₁₀O-OH 加合物, N₂条件下C₁₂H₁₀O-OH衰减的速率常数为(1.86±0.14)×10⁵ s^－1, 在有氧条件下, C₁₂H₁₀O-OH可转化为C₁₂H₁₀O-OHO₂, 衰减的速率常数为(6.6±0.4)×10⁶ s^－1. N₂条件下最终产物为苯酚、2-羟基二苯醚、4-羟基二苯醚、4-硝基二苯醚.     

直链小碳簇Cn(n=3～6)微正则解离速率常数的RRKM理论计算(Ⅰ)

用从头计算法研究小碳簇的解离通道及其动力学.以MP2/6-31G^*精度优化直链C₃,C₄,C₅,C₆及其过渡态的结构,并对它们进行振动分析.在此基础上计算了各解离通道的能垒,并根据RRKM理论估算各个通道的微正则解离速率.计算结果表明,这些小碳簇的解离主要表现为均裂方式.     

加入内标物求解二苯醚OH加合物生成速率常数

往二苯醚(C₁₂H₁₀O)-HNO₂体系中加入内标物苯(C₆H₆), 借助苯和二苯醚与•OH自由基之间的竞争反应, 分析355 nm激光闪光光解C₁₂H₁₀O-C₆H₆-HNO₂体系的衰减动力学曲线, 结合C₁₂H₁₀O-OH adduct的衰减速率常数逆推C₁₂H₁₀O-OH adduct的生成反应速率常数. 借助一种近似方法——微扰论, 通过对＞340 nm处衰减曲线的拟合, 得到C₁₂H₁₀O-OH adduct的生成速率常数为(1.8±0.8)×10¹⁰ L•mol^－1•s^－1.     

乙炔基自由基C2H与氧气反应的密度泛函理论研究

应用量子化学从头算和密度泛函理论(DFT)对C₂H自由基和O₂的反应进行了研究.在B3LYP/6-311G^**水平上优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型,并计算出它们的振动频率和零点振动能(ZPVE).各物种的总能量由CCSD(T)/6-311G^**//B3LYP/6-311G^**给出,并对能量进行了零点能校正.计算结果表明,反应物中自由基C₂H中的边端C进攻O₂形成了中间体1 (HCCOO),中间体1是一个加合产物.由中间体1经过不同的反应通道可以生成不同的产物P₁ (HCO+CO), P₂ (HCCO+O), P₃(CO₂+CH), P₄ (C₂O+OH)和P₅ (2CO+H).反应通道之间存在着竞争机制.其中P₁, P₂是主要产物,其次还有一定比例的P5生成,而产物P₃, P₄的生成几率较低.各条反应通道化学反应热的计算与实验吻合较好.     

266 nm激光光解C2H5SSC2H5产物的激光诱导荧光光谱

有机硫化物是大气主要污染物之一,其在大气中的光解产物还将造成二次污染,除了存在于有机硫化物中, S―S键还存在于胱氨酸等蛋白质中, S―S键的形成和断裂决定该类蛋白质的活性.本工作中,我们研究了用实验室常见的Nd:YAG激光器的四倍频266 nm激光光解C₂H₅SSC₂H₅过程,通过激光诱导荧光(LIF)光谱方法检测乙硫自由基C₂H₅S等光解产物.实验表明266 nm激光主要光解C₂H₅SSC₂H₅的S―S键产生C₂H₅S自由基.本文应用密度泛函理论的Becke3-Lee-Yang-Parr泛函(B3LYP方法)得到C₂H₅SSC₂H₅的S―S键、C―S键和C―C键的解离势能曲线,可知在266 nm光解条件下, C₂H₅SSC₂H₅在基态能够发生S―S键、C―S键解离, C―C键不发生解离.本文采用全活化空间自洽场(CASSCF)方法优化得到态和态的C₂H₅S自由基结构及其跃迁的绝热激发能,以辅助解析实验检测的C₂H₅S自由基的LIF光谱.实验结合理论计算最终得出,本实验266 nm光解条件下, C₂H₅SSC₂H₅主要发生S―S键解离,不排除少量分子发生C―S键解离的可能性.     

新型富勒烯C60有机钴配合物(η2-C60)(η5-RC5H4)CoPPh3 (R=H,CO2Et)的合成及性质研究

鉴于富勒烯C₆₀所具有的缺电子烯烃的特性¹以及CpCo(PPh₃)₂可与烯或炔反应生成钴杂环有机化合物,^2,3 因此我们设想如果用C₆₀代替烯、炔,令其与η⁵-RC₅H₄Co(PPh₃)₂(1) 或η⁵-RC₅H₄Co(PPh₃)(PhC≡CPh)(2)反应,则应得到一类新型的富勒烯C₆₀有机钴杂环化合物。然而与这一设想不同的是,上述反应并未得到预期的C₆₀钴杂环有机物,所得到的却是另一类新型的有机钴C₆₀衍生物(η²-C₆₀)(η⁵-RC₅H₄)CoPPh₃(3).此外,我们发现当3或2同I₂反应时,可生成C₆₀或PhC≡CPh配体被I₂置换产物η⁵-RC₅H₄Co(PPh₃)I₂(4)。     

激光烧蚀Al+与乙醇团簇的反应研究

利用激光烧蚀-分子束法对Al等离子体与乙醇团簇的反应进行了研究.飞行时间质谱测得的主要反应产物有Al⁺(C₂H₅OH)_n (n=3～10)与H⁺(C₂H₅OH)_n (n=1～14)团簇正离子和(C₂H₅OH)_n(H₂O)OH^- (n=0～8)团簇负离子.实验发现,烧蚀产生的Al等离子体与脉冲分子束的不同位置反应,对团簇离子的类别、大小及强度分布均产生很大影响.Al等离子体与脉冲分子束的前段反应,主要产生金属-复合物团簇离子Al⁺(C₂H₅OH)_n,且信号较强;Al等离子体与脉冲分子束的中段及后段反应,主要产生质子化团簇离子H⁺(C₂H₅OH)_n和团簇负离子(C₂H₅OH)_n(H₂O)OH^-,同时还出现强度较小的其他水合团簇离子,如H⁺(H₂O)m(C₂H₅OH)_n (m=1～2)等.     

Dissociative electron attachment to di-tert-butylperoxide, artemisinin, and beta-artemether

The gas-phase dissociative electron attachment spectra of di-tert-butylperoxide (DBP) and the antimalarial polycyclic peroxides artemisinin and beta-artemether are presented for the first time. The total anion currents measured at the walls of the collision chamber and the mass selected anion currents are reported in the 0-6 eV energy range. Electron attachment to DBP produces an intense current, peaking at 1.3 eV, due to the C4H9O- negative fragment, in line with the strongly O-O antibonding character of the singly occupied orbital of the parent molecular anion and the small (if any) thermodynamic energy threshold predicted by B3LYP calculations for the formation of this anion fragment. A five times less intense signal, with m/e = 57 and a maximum at 0.7 eV, is also observed. The calculations exclude that this signal can be associated with the C4H9- negative fragment, whereas they support its assignment to the C3H5O- species, generated by simultaneous dissociation and loss of a methane molecule from the parent molecular anion. In DBP, artemisinin, and beta-artemether, currents corresponding to the parent molecular anion are not detected, indicating that its survival time is shorter than the time required (about 10-6 s) to pass through the mass filter. In the latter two compounds, where simple O-O bond breaking does not generate separate fragments, the anion currents are much weaker than in DBP and the maximum total anion current peaks at zero energy.     

氧负离子与乙烯自由基反应的理论研究

在G3MP2B3理论水平下研究了氧负离子与乙烯自由基的反应机理. 反应入口势能面的刚性扫描显示: 对于不同的初始反应取向, 体系存在3种不同的反应机理, 分别对应直接脱水、插入反应和直接键合成中间体通道. 其中, 通过插入反应形成的富能中间体[CH2＝C—OH]－及键合中间体[CH2＝CHO]－都可以进一步经异构化和解离生成其它各种可能产物, 如C2H－＋H2O, OH－＋CH2C和 ＋CO产物通道. 基于计算得到的反应势垒的相对高度, 直接脱水反应显然是该反应体系最主要的产物通道, 同时我们还结合Mulliken电荷布居分析研究了其中涉及的电子交换过程. 由此, 计算结果证实了以往OH－与C2H2反应的实验研究结果. 此外, 还对比了该反应体系、氧原子与乙烯自由基、氧负离子与乙烯分子三个反应的不同机理.     

A theoretical and computational study of the anion, neutral, and cation Cu(H(2)O) complexes

An ab initio investigation of the potential energy surfaces and vibrational energies and wave functions of the anion, neutral, and cation Cu(H(2)O) complexes is presented. The equilibrium geometries and harmonic frequencies of the three charge states of Cu(H(2)O) are calculated at the MP2 level of theory. CCSD(T) calculations predict a vertical electron detachment energy for the anion complex of 1.65 eV and a vertical ionization potential for the neutral complex of 6.27 eV. Potential energy surfaces are calculated for the three charge states of the copper-water complexes. These potential energy surfaces are used in variational calculations of the vibrational wave functions and energies and from these, the dissociation energies D(0) of the anion, neutral, and cation charge states of Cu(H(2)O) are predicted to be 0.39, 0.16, and 1.74 eV, respectively. In addition, the vertical excitation energies, that correspond to the 4 (2)P<--4 (2)S transition of the copper atom, and ionization potentials of the neutral Cu(H(2)O) are calculated over a range of Cu(H(2)O) configurations. In hydrogen-bonded, Cu-HOH configurations, the vertical excitation and ionization energies are blueshifted with respect to the corresponding values for atomic copper, and in Cu-OH(2) configurations where the copper atom is located near the oxygen end of water, both quantities are redshifted.     

Electron attachment to the hydrogenated Watson-Crick guanine cytosine base pair (GC+H): conventional and proton-transferred structures

The anionic species resulting from hydride addition to the Watson-Crick guanine-cytosine (GC) DNA base pair are investigated theoretically. Proton-transferred structures of GC hydride, in which proton H1 of guanine or proton H4 of cytosine migrates to the complementary base-pair side, have been studied also. All optimized geometrical structures are confirmed to be minima via vibrational frequency analyses. The lowest energy structure places the additional hydride on the C6 position of cytosine coupled with proton transfer, resulting in the closed-shell anion designated 1T (G(-)C(C6)). Energetically, the major groove side of the GC pair has a greater propensity toward hydride/hydrogen addition than does the minor grove side. The pairing (dissociation) energy and electron-attracting ability of each anionic structure are predicted and compared with those of the neutral GC and the hydrogenated GC base pairs. Anion 8T (G(O6)C(-)) is a water-extracting complex and has the largest dissociation energy. Anion 2 (GC(C4)(-)) and the corresponding open-shell radical GC(C4) have the largest vertical electron detachment energy and adiabatic electron affinity, respectively. From the difference between the dissociation energy and electron-removal ability of the normal GC anion and the most favorable structure of GC hydride, it is clear that one may dissociate the GC anion and maintain the integrity of the GC hydride.     

Products of the addition of water molecules to Al3O3- clusters: structure, bonding, and electron binding energies in Al3O4H2-, Al3O5H4-, Al3O4H2, and Al3O5H4

Two stable products of reactions of water molecules with the Al3O3- cluster, Al3O4H2- and Al3O5H4-, are studied with electronic structure calculations. There are several minima with similar energies for both anions and the corresponding molecules. Dissociative absorption of a water molecule to produce an anionic cluster with hydroxide ions is thermodynamically favored over the formation of Al3O3-(H2O)n complexes. Vertical electron detachment energies of Al3O4H2- and Al3O5H4- calculated with ab initio electron propagator methods provide a quantitative interpretation of recent anion photoelectron spectra. Contrasts and similarities in these spectra may be explained in terms of the Dyson orbitals associated with each transition energy.     

Theoretical study of the benzyl+O2 reaction: kinetics, mechanism, and product branching ratios

Ab initio calculations at the level of CBS-QB3 theory have been performed to investigate the potential energy surface for the reaction of benzyl radical with molecular oxygen. The reaction is shown to proceed with an exothermic barrierless addition of O2 to the benzyl radical to form benzylperoxy radical (2). The benzylperoxy radical was found to have three dissociation channels, giving benzaldehyde (4) and OH radical through the four-centered transition states (channel B), giving benzyl hydroperoxide (5) through the six-centered transition states (channel C), and giving O2-adduct (8) through the four-centered transition states (channel D), in addition to the backward reaction forming benzyl radical and O2 (channel E). The master equation analysis suggested that the rate constant for the backward reaction (E) of C6H5CH2OO-->C6H5CH2+O2 was several orders of magnitude higher that those for the product dissociation channels (B-D) for temperatures 300-1500 K and pressures 0.1-10 atm; therefore, it was also suggested that the dissociation of benzylperoxy radicals proceeded with the partial equilibrium between the benzyl+O2 and benzylperoxy radicals. The rate constants for product channels B-D were also calculated, and it was found that the rate constant for each dissociation reaction pathway was higher in the order of channel D>channel C>channel B for all temperature and pressure ranges. The rate constants for the reaction of benzyl+O2 were computed from the equilibrium constant and from the predicted rate constant for the backward reaction (E). Finally, the product branching ratios forming CH2O molecules and OH radicals formed by the reaction of benzyl+O2 were also calculated using the stationary state approximation for each reaction intermediate.     

Temperature dependences for the reactions of O- and O2- with O2(a1Deltag) from 200 to 700 K

Rate constants and product ion distributions for the O- and O2- reactions with O2(a 1Deltag) were measured as a function of temperature from 200 to 700 K. The measurements were made in a selected ion flow tube (SIFT) using a newly calibrated O2(a 1Deltag) emission detection scheme with a chemical singlet oxygen generator. The rate constant for the O2- reaction is approximately 7 x 10(-10) cm3 s-1 at all temperatures, approaching the Langevin collision rate constant. Electron detachment was the only product observed with O2-. The O- reaction shows a positive temperature dependence in the rate constant from 200 to 700 K. The product branching ratios show that almost all of the products at 200 K are electron detachment, with an increasing contribution from the slightly endothermic charge-transfer channel up to 700 K, accounting for 75% of the products at that temperature. The increase in the overall rate constant can be attributed to this increase in the contribution the endothermic channel. The charge-transfer product channel rate constant follows the Arrhenius form, and the detachment product channel rate constant is essentially independent of temperature with a value of approximately 6.1 x 10(-11) cm3 s-1.     

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.     

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.     

钒氧阴离子团簇与小分子碳氢化合物反应的实验和理论研究

为了在分子层次上揭示相关催化反应的机理, 人们对过渡金属氧化物团簇与碳氢化合物分子反应进行了大量研究. 相比于过渡金属氧化物团簇阳离子, 阴离子对一些碳氢化合物的活性弱得多, 因此研究还很少. 在本工作中, 我们通过激光溅射产生钒氧团簇阴离子VxOy, 产生的团簇在接近热碰撞条件下与烷烃(C2H6和C4H10)以及烯烃(C2H4和C3H6) 在一个快速流动反应管中进行反应, 飞行时间质谱用来检测反应前后的团簇分布. 在VxOy与烷烃的反应中, 生成了产物V2O6H-和V4O11H-; 在与烯烃的反应中, 产生了相应的吸附产物V4O11X-(X=C2H4或C3H6). 密度泛函理论计算表明: V2O-6和V4O-11可以活化烷烃(C2H6和C4H10)的C—H键, 也可以与烯烃(C2H4和C3H6)发生3+2环化加成反应形成一个五元环结构(-V-O-C-C-O-), C—H键活化与环加成反应都需经历可以克服的反应能垒. 理论计算与实验观测结果相符合. V2O-6和V4O-11团簇都具有氧原子自由基(O·或O-)的成键特征, 活性O-物种也经常出现在钒氧催化剂表面, 因而本研究在分子水平上, 揭示了表面活性氧物种与碳氢化合物反应的机理.