O-与CH3CN反应机理的密度泛函理论研究

采用G3MP2B3方法研究了氧负离子与乙腈反应的势能剖面.在(U)B3LYP/6-31+G(d,p)理论水平下分别优化了该反应势能面上反应物、产物、中间体和过渡态的分子结构,采用G3MP2B3方法校正了这些关键点的能量. 势能面上的各个反应路径均通过针对过渡态的內禀反应坐标理论计算加以确定. 分别考察了四个可能的热力学产物通道,即质子转移、氢原子转移、H₂⁺转移和双分子亲核取代反应途径. 其中,经H₂⁺转移生成H₂O的反应通道为该反应的主要产物通道.     

F+H2O/D2O→HF+OH反应的准经典轨迹研究：能垒、反应物转动激发和同位素取代的影响 (cited: 4)

在新构建的含旋轨耦合校正的FH₂O基态势能面上,采用准经典轨迹方法详细研究了F+H₂O/D₂O→HF/DF+OH/OD的反应动态学．氢和氘抽取反应经过较低的类反应物过渡态直接发生反应,生成振动激发的HF/DF和内能较低的OH/OD产物．由于新构建的势能面能垒较低,得到的积分反应截面与实验值吻合．但新势能面对产物态分布和模式选择性影响较小．理论计算结果显示H2O的转动态激发对反应有很强的促进作用,说明其与反应坐标耦合紧密．     

硫酸催化乙二醛气体相水化反应机理和速率常数理论计算研究

采用M06-2X和CCSD(T)高阶量化计算和传统过渡态理论研究硫酸催化乙二醛气体相水化反应.对HCOCHO+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O+H₂O, HCOCHO+H₂O...H₂SO₄和HCOCHO+H₂O+H₂SO₄五个路径的反应机理和速率常数进行了研究.计算结果表明硫酸具有较强的催化能力,能显著减小乙二醛水化反应的能垒,在CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)理论水平,当硫酸分子参与乙二醛水化反应时,反应能垒从37.15 kcal/mol减少至7.08 kcal/mol.在室温条件下,硫酸催化乙二醛水化反应的反应速率1.34×10^-11 cm³/(molecule.s),是等量水分子参与乙二醛水化反应的速率的10¹²倍,大于乙二醛与OH自由基反应的反应速率1.10×10^-11 cm³/(molecule.s).这表明大气条件下,硫酸催化乙二醛水化反应可以发生,同乙二醛与OH自由基反应相竞争.     

OH+C2H3F的反应机理及产物支化比反应的理论研究

本文对HOC₂H₃F可能解离通道的势能面进行从头算CCSD(T)/CBS//B3LYP/6-311G(d，p)计算，同时对速率常数进行Rice-Ramsperger-Kassel-Marcus计算. 生成主要产物CH₂CHO+HF最有利的反应途径是OHC₂H₃F→i2→TS14→i6→TS9→i3→TS3→CH₂CHO+HF，其中速率决定步骤是HF通过TS11从CO桥接位置解离，能量比反应物高3.8 kcal/mol. 借助中间态TS14，F原子从C_α迁移到C_β位置生成CH₂O+CH₂F，然后通过中间态TS16，H从O迁移到C_α位置；通过中间态TS5，C-C键断裂生成产物，其能量比反应物低1.8 kcal/mol，比TS11低4.0 kcal/mol.     

气相中自由基OH在不同催化剂下对甲酰氟FCHO进行提氢反应的理论性研究

分别在水、甲酸和硫酸存在的情况下,通过CCSD(T)//M06-2X/6-311++G(3df,3pd)的理论方法,对大气中自由基OH提取甲酰氟FCHO上的氢进行了反应机理和动力学的研究.计算结果表明相对于反应物,加入催化剂的过渡态的能垒从3.64 kcal/mol分别下降到-2.89、-6.25和-7.76 kcal/mol,表明水、甲酸和硫酸在甲酰氟FCHO和自由基OH提氢反应中起了重要作用.通过运用具有Eckart隧道校正的传统过渡态理论计算出的动力学数据表明通道X...FCHO+OH(X=H₂O, HCOOH,或者H₂SO₄)要比通道X...OH+FCHO更有利于反应的发生.催化剂水、甲酸和硫酸的加入使甲酰氟FCHO 和自由基OH提氢反应的速率常数要比不加催化剂时小,说明了催化剂的加入不能促进大气中甲酰氟FCHO和自由基OH的反应.     

Polymerization Mechanism of α-Linear Olefin

利用密度泛函理论在B3LYP方法6-31G水平上对α-直链烯烃在TiCl₃/AlEt₂Cl催化体系的链增长规律进行了相应的计算．对反应物、产物以及各种可能的中间体和过渡态进行了全参数优化,在同一理论水平上对势能面上的全部驻点进行了振动频率分析,并从过渡态分别向反应物和产物方向进行了内禀反应坐标计算．计算结果表明,在TiCl₃/AlEt₂Cl催化剂优化的构型上首先形成配位化合物,进而形成过渡态,过渡态与配位化合物的能量差为40.687 kJ/mol,最后是双键打开和Ti-C(4)断裂,从而完成整个聚合反应历程．计算结果也初步表明随着α-直链烯烃碳原子数的增加,链增长机理未发生本质变化．由聚合反应活化能与α-直链烯烃碳原子数的关系可以看出,碳原子数为6～10时反应活化能较低,是聚合反应合成减阻剂的最佳选择．     

O(1D)和CD4反应的准经典轨线

在新的全域势能面上, 用准经典轨线方法细致地研究了O(¹D)+CD₄多通道化学反应的动力学．这个势能面是用交换不变多项式方法基于MRC+Q/aug-cc-pVTZ从头算点拟合得到的．通过计算得到了产物OD+CD₃、D+CD₂OD/CD₃O和D₂+DCOD/D₂CO的分支比、平动能分布以及角度分布,结果显示理论与实验吻合得较好, 从而说明了这个反应的同位素取代效应很小． 研究表明,O(¹D)+CD₄反应是经过陷入的抽取机理发生的： 最初主要通过D原子的抽取,并不是之前人们认为的直接C-D键的插入形成CD3OD中间物后再进而解离成各个产物通道．     

凝聚态硝基甲烷分解机理的密度泛函研究

用密度泛函理论在B3LYP/6-311++G(2d,2P)计算水平上对最低单态和最低三态的硝基甲烷分子进行了分子动力学计算分析,发现:基态硝基甲烷分子沿C-N键分解生成硝基和甲基反应通道上不存在过渡态,只能是在能量足够高的时候造成C-N键的断裂,键离解能为53.4kcal/mol;硝基甲烷分子在最低三态沿C-N键分解生成硝基和甲基的反应通道上,有一个活化能为87.8kcal/mol的能垒.计算得到硝基甲烷分子从基态到最低三态分解反应发生所需要的总能量为144.58kcal/mol.这个数值与硝基甲烷材料的电子碰撞实验在193nm处有强吸收峰的结论相符合.依据多声子迁移理论,结合硝基甲烷分子在最低三态动力学分解的可能性,可以认为在相同条件下,硝基甲烷材料在撞击条件下,分子沿CN键分裂生成硝基和甲基的反应在最低三态分子分解的可能性较大.文章用量化计算从分子构型、频率分析和势能面扫描方面对分析结论进行了加强和确定,并且,依据多声子迁移理论对硝基甲烷分子基态键离解过程、基态到三态激发过程和最低三态活化过程中的声子迁移进行了初步分析.     

凝聚态硝基甲烷分解机理的密度泛函研究

用密度泛函理论在B3LYP/6-311++G（2d,2P）计算水平上对最低单态和最低三态的硝基甲烷分子进行了分子动力学计算分析,发现,硝基甲烷分子基态沿C-N键分解生成硝基和甲基反应通道上不存在过渡态,只能是在能量足够高的时候造成C-N键的断裂,键离解能为53.4kcal/mol;硝基甲烷分子在最低三态沿C-N键分解生成硝基和甲基的反应通道上,有一个活化能为87.8kcal/mol的能垒。计算得到硝基甲烷分子从基态到最低三态份分解反应发生所需要的总能量为144.58kcal/mol.这个数值与硝基甲烷材料的电子碰撞实验在193nm处的有强吸收峰的结论相符合。依据多声子迁移理论,结合硝基甲烷分子在最低三态动力学分解的可能性,可以认为在相同条件下,硝基甲烷材料在撞击条件下,分子沿C-N键分裂生成硝基和甲基的反应在最低三态分子分解的可能性较大。文章用量化计算从分子构型、频率分析和势能面扫描方面对分析结论进行了加强和确定。并且,依据多声子迁移理论对硝基甲烷分子基态键离解过程、基态到三态激发过程和最低三态活化过程中的声子迁移进行了初步分析。     

CL20/BTF共晶高温热分解ReaxFF/lg分子动力学模拟

用ReaxFF/lg反应力场模拟CL20/BTF共晶在2000~3000 K高温条件下的热分解过程,获得了势能和物种数的演化、初始反应路径及热分解产物等详细信息。通过指数函数对势能的演化曲线进行拟合得到反映特征时间等参数,采用经典的Arrhenius反应速率方程描述总包反应,获得CL20/BTF共晶的活化能E_a=60.8 kcal/mol。研究得到CL20/BTF共晶热分解的初始路径,CL20分子中N-NO₂首先断裂,在热分解起始阶段占主导作用。在不同温度条件下,CL20分子均在BTF分子前完全分解。CL20/BTF共晶的主要产物为NO₂、NO、NO₃、HNO、N₂、H₂O、CO₂、O₂、N₂O、HONO 等。温度对产物均产生一定程度的影响.     

Isomers of OCS and their reaction with H2O on singlet potential energy surface

The isomers of the carbonyl sulfide (OCS) molecule are investigated in detail at CCSD(T)/cc-pVTZ//MP2/6-311++G(2d,2p) level of theory. One cyclic isomer was identified along with three different linear minima of the OCS molecule. Three interconversion transition states were also located between cyclic and linear forms of OCS. Among these four isomers, the singlet potential energy surface (PES) for the molecule–molecule reaction between the three most energetically favoured isomers of OCS and H₂O has been explored theoretically at the CCSD(T)/cc-pVTZ//MP2/6-311++G(2d,2p) level. This singlet PES comprises of three paths. Path 1 is the reaction of linear OCS molecule with water producing the major product P1 (CO₂?+?H₂S), minor product P2 (S?+?HCOOH) and two isomers via 14 minima and 15 transition states. The Path 2 is an isomerization process in which cyclic isomer of OCS reacts with water molecule via another initial barrierless aduct producing five isomers of the OCS–H₂O system through five interconversion transition states. The reaction of linear COS isomer with water is shown in Path 3. This path produces the radicals SH and COOH from another COS–H₂O complex via a transition state. Among these three products, the product P1 is energetically most favoured. The overall exothermicity of the product channels for the formation of major product P1 on PES is calculated to be about 10.60?kcal/mol possessing initial high entrance barriers of 45.48 and 55.47?kcal/mol in two possible pathways. As the process is favoured thermodynamically but not kinetically, the reaction is expected to be very slow.     

Theoretical study on structures and stability of SiC3S isomers

Various levels of calculations are carried out to explore the potential energy surfaces (PES) of singlet and triplet SiC₃S, a molecule of potential interest in interstellar chemistry. At the DFT/B3LYP/6-311G(d) level, a total of 57 minimum isomers and 92 interconversion transition states are located. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311?+?G(2df) single-point energy calculations. At the QCISD level, the lowest-lying isomer is the chain-like SiCCCS ³ 1 (0.0?kcal/mol) with a great kinetic stability of 54.1?kcal/mol. In addition, ring isomers CC-cCSSi ¹ 9 (19.8?kcal/mol), S-cCCCSi ¹ 12 (30.4?kcal/mol), S-cCCSiC ¹ 18 (9.4?kcal/mol), S-cSiCCC ¹ 21 (34.4?kcal/mol) and cage-like isomer cage-SiSCCC ¹ 23 (51.8?kcal/mol) also possess considerable kinetic stability (more than 10.0?kcal/mol). As a result, these six isomers are predicted to be possible candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the SiCCCS are discussed. The predicted structure and spectroscopic properties for it are expected to be informative for the identification of SiC₃S and even larger SiC _n S species either in laboratory or in space.     

Is it possible to synthesize organic Ar compound? a theoretical study

The currently synthesized noble gas (Ng) molecules are mostly xenon or krypton compounds. HArF is the only experimentally prepared compound containing a light Ng atom. In this work, a new argon compound with the formula HArC₄CN, was predicted to be theoretically stable (5.66 kcal/mol at ROCCSD(T)/6-311++g(2d,2p) level of theory). Two decomposition transition states were found, i.e. the 3-body and 2-body decomposition, which produces H, Ar and C₄CN or HC₄CN and Ar respectively. The HArC4CN molecule is meta-stable, but the low energy barrier between the stable molecule and the 3-body transition state makes it possible to synthesize from the three fragments and the high energy barrier between the minimum and the 2-body transition state prevented it from decomposing. Natural bond orbital (NBO) and electron localization function (ELF) analysis show a strong ionic bond between Ar and C atoms whereas covalent between Ar and H. Compared with previous work, it is the conjugation effect of ?C₄CN as well as the its electronegativity that activates the noble gas atom and results in a stable noble gas compound.     

Theoretical studies on [2 + 2 + 2] reaction mechanisms of three ethynes. More accurate estimation of activation energy

The mechanisms of the [2 + 2 + 2] cycloaddition reaction of three ethyne molecules were studied by ab initio molecular orbital and density functional methods. The transition states range from that of the concerted mechanism with D_3h symmetry to that of the stepwise mechanism with C₂ symmetry. The transition state structure and the activation energy depend on the basis set and computational method employed in the analysis. The activation energy barrier was determined to be in the range of 36–44 kcal/mol. The activation energy determined by various methods corresponds to the interaction energy, which is related to the electron correlation energy. The best estimation of the activation energy barrier is 41.6 kcal/mol, achieved from the relation between the interaction energy and the activation energy. Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanism of 4‐methyl‐1,2,4‐triazol‐3‐thiole reaction with formaldehyde. A DFT study

Contrary to the typical nucleophilic substitution, occurring on the sulfur atom of 4‐methyl‐1,2,4‐ triazol‐3‐thiole, the reaction with formaldehyde leads to the formation of the N? C bond rather than the S? C bond. The mechanism of this reaction has been characterized theoretically. Calculations indicate that the reaction proceeds via a cyclic transition state involving one solvent molecule with the Gibbs free activation energy of only 2 kcal/mol. The alternative pathway that leads to the S? C bond formation is about 5 kcal/mol more energetically demanding. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical investigation on the excited‐state intramolecular proton transfer mechanism of 2‐(2′‐benzofuryl)‐3‐hydroxychromone

Spectroscopic studies on excited‐state proton transfer of a new chromophore 2‐(2′‐benzofuryl)‐3‐hydroxychromone (BFHC) have been reported recently. In the present work, based on the time‐dependent density functional theory (TD‐DFT), the excited‐state intramolecular proton transfer (ESIPT) of BFHC is investigated theoretically. The calculated primary bond lengths and angles involved in hydrogen bond demonstrate that the intramolecular hydrogen bond is strengthened. In addition, the phenomenon of hydrogen bond reinforce has also been testified based on infrared (IR) vibrational spectra as well as the calculated hydrogen bonding energies. Further, hydrogen bonding strengthening manifests the tendency of excited state proton transfer. Our calculated results reproduced absorbance and fluorescence emission spectra of experiment, which verifies that the TD‐DFT theory we used is reasonable and effective. The calculated Frontier Molecular Orbitals (MOs) further demonstrate that the excited state proton transfer is likely to occur. According to the calculated results of potential energy curves along O―H coordinate, the potential energy barrier of about 14.5 kcal/mol is discovered in the S₀ state. However, a lower potential energy barrier of 5.4 kcal/mol is found in the S₁ state, which demonstrates that the proton transfer process is more likely to happen in the S₁ state than the S₀ state. In other words, the proton transfer reaction can be facilitated based on the photo‐excitation effectively. Moreover, the phenomenon of fluorescence quenching could be explained based on the ESIPT mechanism. Copyright © 2015 John Wiley & Sons, Ltd.     

Interaction of Ga<Subscript>3</Subscript> cluster with molecular hydrogen: combined DFT and CCSD(T) theoretical study

We have explored the lowest doublet and quartet potential energy surfaces (PES) for the reaction of gallium trimer with H₂. This reaction was studied experimentally by Margrave and co-workers in a noble gas matrix. The detailed reaction paths ending up with the low-energy Ga₃H₂ hydride isomers have been predicted based on the high level ab initio coupled-cluster calculations (CCSD(T)) with large basis set. We have found that the reaction occuring on the lowest doublet PES is described by the activation barrier for H₂ cleavage of about 15 kcal/mol, consistent with experiment. In the most stable Ga₃H₂ hydride structure, whose formation is exothermic by 15 kcal/mol, both H atoms assume three-fold bridged positions. The diterminal planar structure of Ga₃H₂, proposed experimentally from the observed IR spectra, is found to be only 1 kcal/mol less stable than the dibridged form.     

The ESIPT mechanism of dibenzimidazolo diimine sensor: a detailed TDDFT study

Spectroscopic investigations on excited state proton transfer of a new dibenzimidazolo diimine sensor (DDS) were reported by Goswami et al. recently. In our present work, based on the time‐dependent density functional theory (TDDFT), the excited‐state intramolecular proton transfer (ESIPT) mechanism of DDS is studied theoretically. Our calculated results reproduced absorption and fluorescence emission spectra of the previous experiment, which verifies that the TDDFT method we adopted is reasonable and effective. The calculated dominating bond lengths and bond angles involved in hydrogen bond demonstrate that the intramolecular hydrogen bond is strengthened. In addition, the phenomenon of hydrogen bond reinforce has also been testified based on infrared vibrational spectra. Further, hydrogen bonding strengthening manifests the tendency of ESIPT process. The calculated frontier molecular orbitals further demonstrate that the excited state proton transfer is likely to occur. According to the calculated results of potential energy curves along O–H coordinate, the potential energy barrier of about 5.02 kcal/mol is discovered in the S₀ state. However, a lower potential energy barrier of 0.195 kcal/mol is found in the S₁ state, which demonstrates that the proton transfer process is more likely to happen in the S₁ state than the S₀ state. In other words, the proton transfer reaction can be facilitated based on the photo‐excitation effectively. Moreover, the phenomenon of fluorescence quenching could be explained based on the ESIPT mechanism. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrogen bond and internal rotations barrier: DFT study on heavier group‐14 analogues of formamide

A theoretical study on heavier group‐14 substituting effect on the essential property of formamide, strong hydrogen bond with water and internal rotational barrier was performed within the framework of natural bond orbital (NBO) analysis and based on the density functional theory calculation. For heavier group‐14 analogues of formamide (YHONH₂, Y = Si, Ge and Sn), the n_N–π_Y=O conjugation strength does not always reduce as Y becomes heavier, for example, silaformamide and germaformamide have similar strength of delocalization. Heavier formamides prefer being H‐bond donors to form FYO–H₂O complexes to being H‐bond acceptors to form FYH–H₂O complexes. The NEDA analysis indicates that H‐bond energies of FYO–H₂O complexes increase as moving down group 14 due to concurrently stronger charge transfer (CT) and electrostatic attraction and for the FYH–H₂O complexes H‐bond strengths are similar. The model of CTs from FYO to H₂O differs from that at FYH–H₂O complexes, which are contributed not only by aligning lone‐pair orbital of O but also by another lone‐pair orbital. At two lowest lying excited states (the triplet and S₁ excited states), formamide and its heavier analogues form double H‐bonds with H₂O molecule at the same time. The barrier heights of internal rotation become gradually low from C to Sn, formamide (15.73 kcal/mol) > silaformamide (11.73 kcal/mol) > germaformamide (9.45 kcal/mol) > stannaformamide (7.50 kcal/mol) at the CCSD(T)/aug‐cc‐pVTZ//B3LYP/cc‐pVTZ level. NBO analysis indicates that the barrier does not only come from the n_N→π*_YO conjugation, and for heavier analogues of formamide, the n_N→σ*_YO hyperconjugation effect and steric effect considerably contribute to the overall rotational barrier. Copyright © 2013 John Wiley & Sons, Ltd.     

理论研究氧原子与富勒烯C60(Ih)的相互作用

运用密度泛函理论(DFT)方法,研究了异构体C60O[6,6]与C60O[5,6]之间的重排反应机理。结果显示: 它们之间的反应路径是经过一个过渡态没有中间体的一步反应。C60O[6,6] 转化成C60O[5,6]的反应能垒是42.7 kcal*mol-1,在反方向,C60O[5,6]转化成C60O[6,6]的反应能垒是47.3 kcal*mol-1,同时,扫描出氧原子在富勒烯C60(Ih)表面的势能面（PEC）,以详细显示异构体C60O[6,6]与C60O[5,6]之间的重排反应机理。