高压下固相硝基甲烷分解的分子动力学计算

基于ReaxFF, 采用NVT系综和Berendsen方法对0–7 GPa时和2500 K时固相硝基甲烷的 分解过程进行分子动力学计算, 通过分析硝基甲烷发生分解反应生成的碎片数量随时间的变化, 对不同压强下硝基甲烷的分解机理进行研究. 计算结果表明在0–3 GPa时, 初始分解路径为C–N键断裂和硝基甲烷的异构化; 在4–7 GPa 时, 初始分解路径为分子间质子转移和C–N, N–O键的断裂; 在硝基甲烷的第二阶段反应中存在H₂O, NO, NO₂, HONO, 硝基甲烷分子自身的催化反应. 硝基甲烷在高温高压下发生热分解反应生成碳团簇, 且团簇中碳原子的数量和碳团簇的空间构型随着压强的变化而变化. 关键词： ReaxFF 分子动力学 热分解 压强效应 碳团簇     

高温下气相CL-20热分解反应的 分子动力学计算

研究气相CL-20炸药的反应机理及能量释放规律,有助于认识极端条件下含能材料的冲击点火和爆轰等过程。采用反应分子动力学计算方法,研究不同密度和温度下,气相CL-20热分解反应过程。结果表明气相状态时,其初始反应路径为CL-20单分子的N-NO2键断裂生成硝基自由基;第二阶段反应路径为C-C键、C-N键和N-N键等的断裂与生成,发生了质子转移和开环、闭环等基元反应,形成HCN、N2O2、HONO、NO等中间产物;第三阶段反应路径为N2,CO2,H2O和CO等最终稳定产物生成,且生成中间产物的基元反应数量远大于N2、H2O等最终产物生成的基元反应数量。此外,密度和温度还影响了高温下产物的反应速率常数。     

FOX-7的热分解研究

使用原位热红外光谱技术对FOX-7热分解全过程的气相和凝聚相产物进行了原位在线检测,通过非等温热红外动力学处理技术,获得了热分解过程中各特征官能团的断裂分解活化能(kJ·mol-1)如下:C-N键:181.66,-NO2键:235.77,N-H键:170.65.提出了FOX-7可能的两步热分解机理:第一阶段是分子共轭键、分子间(内)氢键的断裂、硝基和亚硝基重排"脱硝"释放出NO,第二阶段是残余碎片分解释放出HCN和NH3,结合TG-DSC-IR联用技术提出了FOX-7热分解的局部化学特性.     

液态硝基甲烷热分解行为及压力效应的第一性原理研究

采用基于密度泛函理论的第一性原理分子动力学方法对液态硝基甲烷的热分解行为进行了模拟,结合各产物布居数随时间的演化,讨论了热分解初期可能发生的3种反应,即分子内/分子间的质子迁移反应和C—N键的断裂.在长时间（30 ps）的模拟过程中,H₂O是主要产物.研究了液态硝基甲烷在不同密度（压力）条件下热分解的动力学行为.发现不同密度（压力）条件下液态硝基甲烷热分解呈现明显不同的变化趋势,并给出了解释. 关键词： 硝基甲烷 分子动力学 热分解 压力效应     

木质素模型化合物热解机理的理论研究

采用密度泛函理论方法B3LYP/6-31G (d,p),对β-O-4型木质素二聚体模化物的热解反应机理进行了量子化学理论研究。提出了三种可能的热解反应途径：Cβ-O键均裂的后续反应、Cα-Cβ键均裂的后续反应以及协同反应。计算了各热解反应途径的标准动力学参数,分析了各种主要热解产物的形成演化机理。计算结果表明,β-O-4型模化物中Cβ-O的键离解能最低,其次是Cα-Cβ的。Cβ-O键均裂的后续反应和协同反应路径（3）是主要的反应路径,而Cα-Cβ键均裂的后续和协同反应路径（1）和（2）是热解过程中主要的竞争反应路径。     

木质素模型化合物热解机理的理论研究

采用密度泛函理论方法 B3LYP/6-31G(d,p),对β-O-4型木质素二聚体模化物的热解反应机理进行了量子化学理论研究.提出了三种可能的热解反应途径:Cβ-O键均裂的后续反应、Cα-Cβ键均裂的后续反应以及协同反应.计算了各热解反应途径的标准动力学参数,分析了各种主要热解产物的形成演化机理.计算结果表明,β-O-4型模化物中Cβ-O的键离解能最低,其次是Cα-Cβ的.Cβ-O键均裂的后续反应和协同反应路径(3)是主要的反应路径,而Cα-Cβ键均裂的后续和协同反应路径(1)和(2)是热解过程中主要的竞争反应路径.     

硝酸酯热分解的机理分析

使用加速量热仪研究硝酸正丙酯（NPN）、硝酸异丙酯（IPN）和硝酸异辛酯（EHN）的热分解过程。分析了在绝热条件下热分解反应动力学, 根据实验数据计算出表观活化能、指前因子和反应热等参数。根据NPN、IPN和EHN热分解的起始温度和反应热数据,给出了三种硝酸酯在75℃时的反应风险指数,分析得到三种物质的热失稳风险度。分别在B3LYP/6-31+G(2df,2p)和B3P86/6-31+G(2df,2p)的理论水平下,计算得到NPN、IPN和EHN的O-NO2键离解能(BDE)。由NPN、IPN和EHN的O-NO2键离解能在很大程度上符合由加速量热仪测试得到的活化能,推知三种硝酸酯的热分解反应只是单分子O-NO2键的均裂反应。     

硝酸酯热分解的机理分析

使用加速量热仪研究硝酸正丙酯（NPN）、硝酸异丙酯（IPN）和硝酸异辛酯（EHN）的热分解过程。分析了在绝热条件下热分解反应动力学, 根据实验数据计算出表观活化能、指前因子和反应热等参数。根据NPN、IPN和EHN热分解的起始温度和反应热数据,给出了三种硝酸酯在75℃时的反应风险指数,分析得到三种物质的热失稳风险度。分别在B3LYP/6-31+G(2df,2p)和B3P86/6-31+G(2df,2p)的理论水平下,计算得到NPN、IPN和EHN的O-NO2键离解能(BDE)。由NPN、IPN和EHN的O-NO2键离解能在很大程度上符合由加速量热仪测试得到的活化能,推知三种硝酸酯的热分解反应只是单分子O-NO2键的均裂反应。     

聚偏氯乙烯热解动力学研究

聚偏氯乙烯的热不稳定性被用作制备含碳材料的前驱体。本工作利用红外光谱在线检测功能，原位测定了聚偏氯乙烯热分解动力学过程的红外谱图，分析并计算了聚偏氯乙烯分子链中C-H和C-C1键断裂的反应活化能，得到了聚偏氯乙烯分解过程的动力学特性。     

吡喃木糖热裂解机理的密度泛函理论研究

采用密度泛函理论理论方法 M062X/6-311++G(d,p),对吡喃木糖的热解反应机理进行了理论计算分析.针对吡喃木糖热解可能发生的化学反应共设计了九条可能的热解路径,并对各路径中的反应物、中间体和过渡态的几何结构进行了能量梯度全优化,并在梯度全优化的基础上计算了各热解反应路径的热力学和动力学参数.文中以两大类方式来设计反应路径:1)木糖首先经过过渡态TS1发生开环反应生成链状中间体2,该步的反应能垒为188.7 kJ/mol,对于中间体2共设计了五种可能的热解反应路径;2)考虑双键同时断裂的情况,木糖先发生脱水反应,接着按C-C和C-O键同时断裂的情况发生开环反应,针于这种情况共设计了四条可能的热解路径.计算结果表明,吡喃木糖热解的主要反应产物有乙醇、乙醛、糠醛、丙酮、酸类、CO_2和CO等小分子化合物.     

Thermal decomposition of 2,4,6-triazido-1,3,5-triazine

The thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt and a dinonyl phthalate solution is studied by thermogravimetry, manometry, mass spectrometry, and IR spectroscopy. The kinetic and activation parameters of the process are determined. The only gaseous product of the reaction is nitrogen. This fact, along with the structure of the condensed residue formed during the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in the melt, are indicative of the abstraction of a nitrogen molecule from an azide group at the initial stage and of the subsequent reactions leading to the formation of a planar network of polyconjugated bonds between C and N atoms. For the thermal decomposition of 2,4,6-triazido-1,3,5-triazine in solution the preexponential factor and activation energy are found to be 10^12.8 s^–1 and 34100 cal/mol, respectively, which are characteristic of the thermal decomposition of most azides. To explain why these parameters are substantially higher for the reaction in the melt (10^17.4 s^–1 and 42300 cal/mol), it is assumed that, in this case, the process proceeds by the polymerization (polycondensation) mechanism to form twodimensional networks, with the apparent kinetic parameters being effective quantities. Based on these data, it is concluded that the high sensitivity of 2,4,6-triazido-1,3,5-triazine to external influences is of kinetic nature.     

Step-wise decomposition process of azobenzene self-assembled monolayers

The step-wise decomposition of 4-(12-(dodecyldithio)dodecyloxy)azobenzene (AzoC24) in self-assembled monolayer (SAMs) on Au(1 1 1) was observed by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) under the ultra-high vacuum (UHV) condition. This decomposition process only occurred after the formation of the SAM.The TD spectra clearly showed two steps of thermal decomposition of the azobenzene moiety. At approximately 450 K, fragments of m/e = 77 and 105 were clearly observed. These fragments were decomposed species obtained by the breakage of the C-N bonds of the azobenzene moiety. At about 490 K, other fragment of m/e = 93 assigned to the phenoxy ion was detected. In order to examine the decomposition process, we measured the S 2p and N 1s XPS of the SAM at various temperatures. The results suggest that diazonium moiety is the first to be decomposed and the remaining structure is desorbed together with breakage of C-O bond between the phenoxy moiety and alkyl chain with increasing temperature.     

Kinetics of radical reactions involved in the gas-phase thermal decomposition of nitrobenzene

The performance of a method for analyzing complex kinetic processes is demonstrated by the example of the thermal decomposition of nitrobenzene in the gas phase. A gradual increase in the number of reactions, determination of the parameters involved, and comparison with experimental data made it possible to construct a minimum mechanism capable of describing the experimental data within the selected pressure range. The rate constants for a number of reactions of radicals with the initial reactant and reaction products were determined.     

The thermal decomposition of azidopyridines

The thermal decomposition of new heteroaromatic polyazides 2,6-diazido-3,5-dicyanopyridine, 2,4,6-triazido-3,5-dicyanopyridine, and 2,3,4,5-tetraazido-6-cyanopyridine was studied by thermogravimetry, volumetry, mass-spectrometry, and IR spectroscopy. Reaction kinetic parameters were determined. The only gaseous product of the thermal decomposition of all the azides studied was nitrogen, its degree of purity was 99.0–99.8 vol %. 2,6-Diazido-3,5-dicyanopyridine and 2,4,6-triazido-3,5-dicyanopyridine had thermal stability and thermal decomposition parameters close to those of the majority of aromatic azides. The mechanism of thermal decomposition of these azides includes the splitting off of the nitrogen molecule at the initial limiting process stage. Subsequent intermolecular reactions with the participation of nitrenes result in the formation of an amorphous substance containing polyconjugated fragments with sp ² hybridization, which form planar two-dimensional networks. 2,3,4,5-Tetraazido-6-cyanopyridine has very low thermal stability; the rate of nitrogen release during its decomposition is almost 1000 times higher than with 2,6-diazido-3,5-dicyanopyridine and 2,4,6-triazido-3,5-dicyanopyridine at comparable temperatures. This was explained by the presence of the ortho azido group (there is no ortho arrangement of azido groups in 2,6-diazido-3,5-dicyanopyridine and 2,4,6-triazido-3,5-dicyanopyridine).     

二元混合工质的氧化分解机理研究

基于量子化学密度泛函理论对低全球变暖潜值工质R152a与R600a进行了氧化分解机理研究. 通过对它们的主要起始反应路径分析及能量变化情况计算,结果表明：R152a与R600a热分解的起始反应可以分为工质自身热分解和与氧气碰撞分解两类,其中工质自身热分解的反应能垒比工质与氧气反应的能垒高,并且R600a比R152a更容易发生氧化分解;在二者混合后的起始反应阶段,R600a更容易先发生分解,而链式反应中R152a与自由基的反应更占优势;两种工质与自由基的反应大部分为放热反应,可以向反应体系提供热量,促进链式反应的进行. 相关结果可为新型混合工质的氧化分解机理研究提供参考.     

Kinetic measurements by variable-temperature photoelectron spectroscopy. The kinetic rate of the bicyclopentadiene to cyclopentadiene reaction in the medium-vacuum region

Using an appropriate reactor and variable-temperature photoelectron spectroscopy (VTPES), the kinetic rate-constant for the duration of bicyclopentadiene to cyclopentadiene is determined as approximately 1.9 s^?1 at 328°C and 0.1 torr. The study constitutes the first application of photoelectron spectroscopy to the quantitative investigation of chemical reactions. The technique might prove useful for the study of thermal decomposition reactions in the medium-vacuum region.     

氢催化的二硝酰胺铵热分解的从头算分子动力学研究

Thermal decomposition of a famous high oxidizer ammonium dinitramide (ADN) under high temperatures (2000 and 3000 K) was studied by using the ab initio molecular dynamics method.Two different temperature-dependent initial decomposition mechanisms were observed in the unimolecular decomposition of ADN,which were the intramolecular hydrogen transfer and N-NO₂ cleavage in N (NO₂)^-.They were competitive at 2000 K,whereas the former one was predominant at 3000 K.As for the multimolecular decomposition of ADN,four different initial decomposition reactions that were also temperature-dependent were observed.Apart from the aforementioned mechanisms,another two new reactions were the intermolecular hydrogen transfer and direct N-H cleavage in NH₄⁺.At the temperature of 2000 K,the N-NO₂ cleavage competed with the rest three hydrogen-related decomposition reactions,while the direct N-H cleavage in NH₄⁺ was predominant at 3000 K.After the initial decomposition,it was found that the temperature increase could facilitate the decomposition of ADN,and would not change the key decomposition events.ADN decomposed into small molecules by hydrogen-promoted simple,fast and direct chemical bonds cleavage without forming any large intermediates that may impede the decomposition.The main decomposition products at 2000 and 3000 K were the same,which were NH₃,NO₂,NO,N₂O,N₂,H₂O,and HNO₂.     

液相硝基甲烷分子振动特性的相干反斯托克斯拉曼散射光谱

构建时间分辨相干反斯托克斯拉曼散射（CARS）光谱系统,从微观层次研究硝基甲烷的分子相干振动动力学特性.实验中采用超连续白光作为斯托克斯光,通过调整斯托克斯光的时间延迟,得到不同振动模式的CARS光谱.通过对振动弛豫曲线的拟合,获得硝基甲烷分子不同振动模式的振动失相时间.结果表明C–H键伸缩振动比C–N键伸缩振动更容易受热声子的影响.在热加载下,硝基甲烷分子的C–H键有望首先被激发并引起初始化学反应.