高压下硝基甲烷分子温度的密度泛函计算

用密度泛函理论在B3LYP/6-311++G(2d,2P)计算水平上对硝基甲烷分子进行了结构优化、频率和热化学分析.发现:在相同温度条件下改变压强,分子熵函数产生了改变,当温度和压强条件相同时,对于不同物质熵函数的改变是相同的.以热力学理论中麦克斯韦关系为基础,通过计算等温过程中分子的熵函数对压强的变化率,用数值拟合方法得到不同压强条件下分子温度的表达式:T=T0+(1-B)[18.3858+0.5392P]V0,式中T0、V0分别表示分子系统初态的温度和体积,T、V分别表示系统在末态的温度和体积,B是体积的压缩比.在选定参数的情况下该表达式可以计算不同压强条件下CHNO含能材料的分子温度.同时,以硝基甲烷为验证,选取基本参数V0和B,计算其在C-J条件对应的爆压14GPa下,分子温度为3461K,对应爱因斯坦温度,相当于3228cm-1的能量,在实验中该能量足以激发硝基甲烷分子内振动能量重新分配过程,有可能激发C-N键的红外振动而引起单分子分解反应的发生.因此,此表达式可用于预测含能材料撞击点火过程单分子分解可能的反应通道.     

固相硝基甲烷相变的第一性原理计算

研究极端条件下固相分子晶体含能材料的相变机理,对于人们认识固相含能材料的爆轰反应有着重要的意义.采用基于校正密度泛函理论的第一性原理方法研究固相硝基甲烷在静水压下的行为.分析晶格参数a,b和c轴随压强的变化,发现在1 GPa到12 GPa时晶格参数出现不连续的变化,表明体系发生相变.在相变时最大的二面角从155.3?增加到177.5?,二面角的增加限制CH3官能团自由旋转,使得C-N和C-H键的键长发生变化.在相变之前,体系主要存在由C-H···O组成的分子间的氢键,而在相变之后存在分子内的H···O和分子间C-H···O组成的氢键.此外通过对硝基甲烷体系的电子结构进行计算,发现相变会影响带隙随压强的变化,而且还会影响费米能级附近的态密度结构.     

三硝基甲烷键离解能和生成焓的理论计算

采用密度泛函(DFT)四种交换/相关函数(B3LYP、B3P86、B3PW91和PBE0)结合不同的基函数,求得了三硝基甲烷C-NO2键的离解能(BDE),并且通过合理选择参考物硝基甲烷,设计等键等电子对反应,计算了气相三硝基甲烷分子的生成焓(HOF).与实验数据进行比较,PBE0/6-31g*计算出的BDE值最好,误差为-2.1 kcal mol-1;PBE0密度泛函结合带极化函数的6-31g基组得到的HOF值与实验值吻合的最好(误差在0.1 kcal mol-1以内).     

硝基甲烷异构化反应势能面的ab initio研究

在B3LYP/ 6 311++G(2d ,2p)水平上 ,优化得到硝基甲烷CH3 NO2 的 10种异构体和 2 3个异构化反应过渡态 ,并用G2MP2方法进行了单点能计算 .根据计算得到的G2MP2相对能量 ,探讨了CH3 NO2 势能面上异构化反应的微观机理 .研究表明 ,反应初始阶段的CH3 NO2 异构化过程具有较高的能垒 ,其中CH3 NO2 的两个主要异构化反应通道 ,即CH3 NO2 →CH3 ONO和CH3 NO2 →CH2 N(O)OH的活化能分别为 2 70 .3和 2 6 7.8kJ/mol,均高于CH3 NO2的C -N键离解能 .因而 ,从动力学角度考虑 ,CH3 NO2 的异构化反应较为不利 .     

单次冲击压缩下液态硝基甲烷的拉曼光谱

在单次冲击压缩实验中,运用高敏度瞬态拉曼光谱技术观测了液态硝基甲烷分子的拉曼光谱. 将该拉曼测量技术与二级轻气炮的实验平台结合起来,获得硝基甲烷分子振动模式的高压动态行为. 硝基甲烷被12 GPa压力冲击时的拉曼光谱可清晰探测,其拉曼振动峰仅仅发生了峰位蓝移和峰宽展宽的变化,未显示出化学变化产生的迹象.     

用多声子迁移模型理论研究硝基甲烷的分解机理

基于多声子迁移模型理论分析了撞击诱导硝基甲烷单分子分解反应可能存在的合理的反应路径。发现：对最低三态和基态的分子选择门模式分别为407cm-1,436cm-1和482cm-1, 616cm-1时,计算得到的相同时间长度上的能量迁移参数分别为5.43×105 J/mol*K ,5.82×105 J/mol*K 和8.22×105 J/mol*K,6.43×105 J/mol*K。而理论计算CH3NO2分子从基态跃迁致最低三态所需能量为2.39×105 J/mol,最低三态分子从C-N键断裂分解为硝基和甲基所需活化能为3.69×105 J/mol;基态的CH3NO2分子从C-N键断裂生成硝基和甲基所需能量为2.24×105 J/mol。因此,能量迁移能够提供足够的能量使CH3NO2分子在基态或者在跃迁至最低三态后从C-N键断裂生成硝基和甲基。这个结论与实验报道的结论基本一致。     

用多声子迁移模型理论研究硝基甲烷的分解机理

基于多声子迁移模型理论分析了撞击诱导硝基甲烷单分子分解反应可能存在的合理的反应路径。发现：对最低三态和基态的分子选择门模式分别为407cm-1,436cm-1和482cm-1, 616cm-1时,计算得到的相同时间长度上的能量迁移参数分别为5.43×105 J/mol*K ,5.82×105 J/mol*K 和8.22×105 J/mol*K,6.43×105 J/mol*K。而理论计算CH3NO2分子从基态跃迁致最低三态所需能量为2.39×105 J/mol,最低三态分子从C-N键断裂分解为硝基和甲基所需活化能为3.69×105 J/mol;基态的CH3NO2分子从C-N键断裂生成硝基和甲基所需能量为2.24×105 J/mol。因此,能量迁移能够提供足够的能量使CH3NO2分子在基态或者在跃迁至最低三态后从C-N键断裂生成硝基和甲基。这个结论与实验报道的结论基本一致。     

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。     

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.     

常压溶剂法合成抗氧剂3114反应热力学和动力学

研究了常压溶剂法一步合成抗氧剂3114反应热力学和动力学过程。控制温度在117±2℃,研究结果表明,反应是零级反应,反应速率常数为k=1．91×10^-3／min,反应的平衡常数为K=138．4（mol／L）^-6,反应活化能Ea=1366J／mol。     

Kinetics for the reaction of phenyl radical with phenylacetylene and styrene

The kinetics for the reactions of C₆H₅ with phenylacetylene and styrene have been measured by CRDS in the temperature range 297-409 K under an Ar pressure of 3.6 Torr. The total rate constants can be given by the following Arrhenius expressions (in units of cm³ mol⁻¹ s⁻¹): k₁(C₆H₅ + C₆H₅C₂H) = 10^13.0±0.1exp [−(2430 ± 150)/RT] and k₂(C₆H₅ + C₆H₅C₂H₃) = 10^13.3±0.1 exp [−(2570 ± 180)/T]. Additional DFT and MP2 calculations have been carried out to assist our interpretation of the measured kinetic data. The addition of C₆H₅ to the terminal CH_x (x = 1 or 2) sites is predicted to be the dominant channel for both reactions. The calculated bimolecular rate constants are in reasonable agreement with experimental values for the temperature range studied.     

丙烷与O(3P)反应机理和动力学的理论研究

The reaction of C₃H₈+O(³P)→C₃H₇+OH is investigated using ab initio calculation and dynamical methods. Electronic structure calculations for all stationary points are obtained using a dual-level strategy. The geometry optimization is performed using the unrestricted second-order Møller-Plesset perturbation method and the single-point energy is computed using the coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations method. Results indicate that the main reaction channel is C₃H₈+O(³P)→i-C₃H₇+OH. Based upon the ab initio data, thermal rate constants are calculated using the variational transition state theory method with the temperature ranging from 298 K to 1000 K. These calculated rate constants are in better agreement with experiments than those reported in previous theoretical studies, and the branching ratios of the reaction are also calculated in the present work. Furthermore, the isotope effects of the title reaction are calculated and discussed. The present work reveals the reaction mechanism of hydrogen-abstraction from propane involving reaction channel competitions is helpful for the under-standing of propane combustion.     

CH2 CHF与臭氧反应机理的量子化学研究

用量子化学MP2方法 ,在 6 311++G(d ,p)基组水平上研究了烯烃CH2 CHF与臭氧反应的机理 ,对氟代乙烯臭氧化反应Criegee机理进行了系统的计算 ,全参数优化了反应过程中反应物、中间体、过渡态和产物的几何构型 ,在QCISD(T) / 6 311++G(d ,p)水平上计算了它们的能量 .并对它们进行了频率分析 ,以确定中间体和过渡态的真实性 .研究结果表明 ,氟代乙烯与臭氧反应沿Criegee机理是可信的、合理的 .同时研究还发现 ,就氟代乙烯与臭氧反应活性而言 ,其控制步骤的位垒较低 ,可以说氟代乙烯与臭氧反应活性较强 ,也就是说氟代乙烯对臭氧的损耗较大 .     

DNA腺嘌呤阳离子自由基脱质子反应机理的研究

Among all the DNA components, extremely redox-active guanine (G) and adenine (A) bases are subject to facile loss of an electron and form cation radicals (G^+· and A^+·) when exposed to irradiation or radical oxidants. The subsequent deprotonation of G^+· and A^+· can invoke DNA damage or interrupt hole transfer in DNA. However, compared with intensive reports for G^+·, studies on the deprotonation of A^+· are still limited at present. Herein, we investigate the deprotonation behavior of A^+· by time-resolved laser flash photolysis. The deprotonation product of A(N₆-H)^· is observed and the deprotonation rate constant, (2.0±0.1)×10⁷ s^-1, is obtained at room temperature. Further, the deprotonation rate constants of A^+· are measured at temperatures varying from 280 K to 300 K, from which the activation energy for the N₆-H deprotonation is determined to be (17.1±1.0) kJ/mol by Arrhenius equation. In addition, by incorporating the aqueous solvent effect, we perform density functional theory calculations for A^+· deprotonation in free base and in duplex DNA. Together with experimental results, the deprotonation mechanisms of A^+· in free base and in duplex DNA are revealed, which are of fundamental importance for understanding the oxidative DNA damage and designing DNA-based electrochemical devices.     

用量子力学方法计算H+H2碰撞的反应几率

利用量子力学耦合通道扭曲波近似法(CCDWA)和三种势能面计算了H+H2碰撞的反应几率,结果发现在相同的势能面下利用CCDWA方法计算的反应几率和公认较好的计算结果符合很好,不同势能面共线势垒高度的差别将引起反应几率的不同.     

Irradiation effect on the activation energy of thermal decomposition of polymers

The present work looks into the aspect of thermal modifications induced in polymers by proton irradiation. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived.     

A study of the activation energy of thermal decomposition of irradiated polymers

The ion irradiation of polymeric solids induces numerous modifications in the polymer properties thus increasing their applicability in various fields. The present work looks into the aspect of thermal modifications induced in the irradiated polymers. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived.     

Kinetics and thermodynamics of reversible disproportionation–comproportionation in redox triad oxoammonium cations – nitroxyl radicals – hydroxylamines

Kinetics and equilibrium of the acid‐catalyzed disproportionation of cyclic nitroxyl radicals R₂NO^? to oxoammonium cations R₂NO⁺ and hydroxylamines R₂NOH is defined by redox and acid–base properties of these compounds. In a recent work (J. Phys. Org. Chem. 2014, 27, 114‐120), we showed that the kinetic stability of R₂NO^? in acidic media depends on the basicity of the nitroxyl group. Here, we examined the kinetics of the reverse comproportionation reaction of R₂NO⁺ and R₂NOH to R₂NO^? and found that increasing in –I‐effects of substituents greatly reduces the overall equilibrium constant of the reaction K₄. This occurs because of both the increase of acidity constants of hydroxyammonium cations K_3H+ and the difference between the reduction potentials of oxoammonium cations E_R2NO+/R2NO? and nitroxyl radicals E_R2NO?/R2NOH. pH dependences of reduction potentials of nitroxyl radicals to hydroxylamines E_1/3Σ and bond dissociation energies D(O–H) for hydroxylamines R₂NOH in water were determined. For a wide variety of piperidine‐ and pyrrolidine‐1‐oxyls values of pK_3H+ and E_R2NO+/R2NO? correlate with each other, as well as with the equilibrium constants K₄ and the inductive substituent constants σ_I. The correlations obtained allow prediction of the acid–base and redox characteristics of redox triads R₂NO^?–R₂NO⁺–R₂NOH. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetics of electrochemical boriding of low carbon steel

In this study, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 mA/cm² in a borax based electrolyte at temperatures ranging from 1123 K to 1273 K for periods of 5-120 min. After boriding, the presence of both FeB and Fe₂B phases were confirmed by the X-ray diffraction method. Cross-sectional microscopy revealed a very dense and thick morphology for both boride phases. Micro hardness testing of the borided steel samples showed a significant increase in the hardness of the borided surfaces (i.e., up to (1700 ± 200) HV), while the hardness of un-borided steel samples was approximately (200 ± 20) HV. Systematic studies over a wide range of boriding time and temperature confirmed that the rate of the boride layer formation is strongly dependent on boriding duration and has a parabolic character. The activation energy of boride layer growth for electrochemical boriding was determined as (172.75 ± 8.6) kJ/mol.