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采用量子化学QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p)方法研究了H2FCS单分子分解反应的微观动力学性质, 构建了反应势能剖面. 利用经典过渡态理论(TST)与变分过渡态理论(CVT)并结合小曲率隧道效应模型(SCT), 分别计算了在200~3000 K温度范围内的速率常数kTST、kCVT和kCVT/SCT. 计算结果表明, H2FCS可经过不同的反应通道生成10种小分子产物, 脱H反应和HF消去反应为标题反应的主反应通道, 其中HF消去反应产物HCS可由两条反应通道生成. 在200~3000 K温度区间内得到三条反应通道的表观反应速率常数三参数表达式分别为 , 和 . 速率常数计算结果显示, 量子力学隧道效应在低温区间对反应速率常数的影响显著, 而变分效应在计算温度范围内可以忽略. 相似文献
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在B3LYP/6-311++G(2df,p)水平下对单分子水参与下的CH_2SH+NO_2反应的微观机理进行了研究.为了获得更准确的能量信息,采用HL复合方法和CCSD(T)/aug-ccpvtz方法进行单点能校正.结果表明,加入单分子水后的CH_2SH+NO_2反应体系,共经过10条不同的反应路径,得到6种反应产物.与裸反应(CH_2SH+NO_2)相比,水分子在反应中起到了明显的正催化作用.不仅使生成产物trans-HONO的能垒(-52.84kJ·mol~(-1))降低了176.94kJ·mol~(-1),而且不需经过复杂的重排和异构化过程便可得到产物cis-HONO.在生成产物cis-HONO通道(Path3和Path4)中,活化能垒分别为143.65和126.70kJ·mol~(-1),而其裸反应的活化能垒却高达238.34kJ·mol~(-1).生成HNO_2的通道中(Path5和Path6)活化能垒分别为295.23和-42.19kJ·mol~(-1).其中Path6的无势垒过程使HNO_2也成为该反应的主要产物.另外,单分子水还可通过氢迁移的方式直接参与CH_2SH+NO_2的反应,活化能垒(TS7-TS10)分别为-10.62,151.03,186.22和155.10kJ·mol~(-1).除直接抽氢通道中的(Path8-Path10)外,其余反应通道均为放热反应,在热力学上是可行的. 相似文献
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在aug-cc-pVTZ基组下采用CCSD(T)和B3LYP方法,研究了H2O2+Cl反应,并考虑在大气中单个水分子对该反应的影响.结果表明,H2O2+Cl反应只存在一条生成产物为HO2+HCl的通道,其表观活化能为10.21kJ·mol-1.加入一分子水后,H2O2+Cl反应的产物并没有发生改变,但是所得势能面却比裸反应复杂得多,经历了RW1、RW2和RW3三条通道.水分子在通道RW1和RW2中对产物生成能垒的降低起显著的负催化作用,而在通道RW3中则起明显的正催化作用.利用经典过渡态理论(TST)并结合Wigner矫正模型计算了216.7-298.2 K温度范围内标题反应的速率常数.结果显示,298.2 K时通道R1的速率常数为1.60×10-13cm3·molecule-1·s-1,与所测实验值非常接近.此外,尽管通道RW3的速率常数kRW3比对应裸反应的速率常数kR1大了46.6-131倍,但该通道的有效速率常数k'RW3却比kR1小了10-14个数量级,表明在实际大气环境中水分子对H2O2+Cl反应几乎没有影响. 相似文献
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H2CO和NO2反应机理的密度泛函理论计算研究 总被引:2,自引:2,他引:2
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. 相似文献
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邻位吡啶自由基多通道分解反应的动力学和反应机理研究 总被引:1,自引:0,他引:1
Utilizing Gaussian94 program package, all species involved in decomposition reactions of o-pyridyl radical were optimized fully at B3LYP/6-311++G^** level. Intrinsic reaction coordinate calculations were employed to confirm the connections of the transition states and products, and transition states were ascertained by the number of imaginary frequency (0 or 1). The reaction mechanism was elucidated by the vibrational mode analysis and electronic population analysis, and the reaction rate constants were calculated with transition state theory. 相似文献
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采用密度泛函B3LYP/6-311G(d,p)方法对CH3F与C2H3的反应体系进行了理论研究,获得了反应的势能面信息及可能的微观机理.在QCISD(T)/6-311++G(d,p)水平上精确计算了各反应物种的单点能.结果表明,除抽提氢反应外,标题反应还存在抽提氟(R1)、消氟化氢(R2)、消氢(R3)和自由基形成(R4)四类反应.在QCISD(T)/6-311++G(d,p)//B3LYP/6-311G(d,p)水平上,R1,R2,R3和R4反应的能垒分别是163.9,152.2,209.8和224.2kJ·mol-1,相应反应能为-56.6,-164.3,-2.7和-156.0kJ·mol-1,所有反应均放热,为热力学允许的反应. 相似文献
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Al-Muhtaseb AH Altarawneh M Almatarneh MH Poirier RA Assaf NW 《Journal of computational chemistry》2011,32(12):2708-2715
The potential energy surface for the unimolecular decomposition of thiophenol (C(6)H(5)SH) is mapped out at two theoretical levels; BB1K/GTlarge and QCISD(T)/6-311+G(2d,p)//MP2/6-31G(d,p). Calculated reaction rate constants at the high pressure limit indicate that the major initial channel is the formation of C(6)H(6)S at all temperatures. Above 1000 K, the contribution from direct fission of the S-H bond becomes important. Other decomposition channels, including expulsion of H(2) and H(2)S are of negligible importance. The formation of C(6)H(6)S is predicted to be strong-pressure dependent above 900 K. Further decomposition of C(6)H(6)S produces CS and C(5)H(6). Overall, despite the significant difference in bond dissociation, i.e., 8-9 kcal/mol between the S-H bond in thiophenol and the O-H bond in phenol, H migration at the ortho position in the two molecules represents the most accessible initial channel. 相似文献
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Theoretical studies of the NTO unimolecular decomposition 总被引:1,自引:0,他引:1
This work studies 39 decomposition paths among 18 intermediates and 14 transition states. Three types of intra-molecular proton migration and the direct scission of C–NO2 were regarded as the initial steps of the unimolecular decomposition of NTO. The activation energies of the radicalization C–NO2 homolysis step are 79.158, 79.781 and 80.652 kcal mol−1. The activation energies of the ionization C–NO−12 scission step are 262.488, 263.138 and 272.278 kcal mol−1. The bottle neck activation energies of the C–NO2H cleavage are 54.936, 63.257 and 71.247 kcal mol−1. Two paths have the smallest bottle neck activation energy. Both of them have two proton migration steps and one internal rotation step prior to C–NO2H cleavage. At lower temperatures, energy accumulated slowly. When the energy is high enough and reaction time is long enough for structure transformation, these two mechanisms should be the most probable decomposition paths. At high temperatures, the shortest (four steps) mechanism which goes through radicalization C–NO2 scission should be the dominant path. There are five tautomers found in this study. Four of them are intra-molecular proton migration tautomers. The other one is an internal rotational tautomer. Their energy barriers for structure transfer are lower than any of the activation energies of the decomposition reactions. It may be regarded as one explanation of the insensitive property of NTO. 相似文献
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The kinetics and mechanism for the unimolecular decomposition of o-nitrotoluene (o-CH(3)C(6)H(4)NO(2)) have been studied computationally at the G2M(RCC, MP2)//B3LYP/6-311G(d, p) level of theory in conjunction with rate constant predictions with RRKM and TST calculations. The results of the calculations reveal 10 decomposition channels for o-nitrotoluene and its six isomeric intermediates, among them four channels give major products: CH(3)C(6)H(4) + NO(2), C(6)H(4)C(H)ON (anthranil) + H(2)O, CH(3)C(6)H(4)O (o-methyl phenoxy) + NO, and C(6)H(4)C(H(2))NO + OH. The predicted rate constants in the 500-2000 K temperature range indicate that anthranil production, taking place initially by intramolecular H-abstraction from the CH(3) group by NO(2) followed by five-membered ring formation and dehydration, dominates at temperatures below 1000 K, whereas NO(2) elimination becomes predominant above 1100 K and CH(3)C(6)H(4)O formation by the nitro-nitrite isomerization/decomposition process accounts for only 5-11% of the total product yield in the middle temperature range 800-1300 K. The branching ratio for CH(2)C(6)H(4)NO formation by the decomposition process of CH(2)C(6)H(4)N(O)OH is negligible. The predicted high-pressure-limit rate constants with the rate expression of 4.10 x 10(17) exp[-37000/T] s(-1) for the NO(2) elimination channel and 9.09 x 10(12) exp[-25800/T] s(-1) for the H(2)O elimination channel generally agree reasonably with available experimental data. The predicted high-pressure-limit rate constants for the NO and OH elimination channels are represented as 1.49 x 10(14) exp[-30000/T] and 1.31 x 10(15) exp[-38000/T] s(-1), respectively. 相似文献
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The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H(2)O-elimination channels have the lowest barriers, and the C-C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H(2)O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C-C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500-2000 K, the calculated rate constant is expressed to be 7.63 × 10(47)T(-10.38) exp(-42262/T) for the channel CH(2)OHCH(2)OH → CH(2)CHOH + H(2)O, and 2.48 × 10(51)T(-11.58) exp(-43593/T) for the channel CH(2)OHCH(2)OH → CH(3)CHO + H(2)O, whereas for the direct bond dissociation reaction CH(2)OHCH(2)OH → CH(2)OH + CH(2)OH the rate constant expression is 1.04 × 10(71)T(-16.16) exp(-52414/T). 相似文献
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The kinetics and mechanisms for the unimolecular dissociation of nitrobenzene and related association reactions C(6)H(5) + NO(2) and C(6)H(5)O + NO have been studied computationally at the G2M(RCC, MP2) level of theory in conjunction with rate constant prediction with multichannel RRKM calculations. Formation of C(6)H(5) + NO(2) was found to be dominant above 850 K with its branching ratio > 0.78, whereas the formation of C(6)H(5)O + NO via the C(6)H(5)ONO intermediate was found to be competitive at lower temperatures, with its branching ratio increasing from 0.22 at 850 K to 0.97 at 500 K. The third energetically accessible channel producing C(6)H(4) + HONO was found to be uncompetitive throughout the temperature range investigated, 500-2000 K. The predicted rate constants for C(6)H(5)NO(2) --> C(6)H(5) + NO(2) and C(6)H(5)O + NO --> C(6)H(5)ONO under varying experimental conditions were found to be in good agreement with all existing experimental data. For C(6)H(5) + NO(2), the combination processes producing C(6)H(5)ONO and C(6)H(5)NO(2) are dominant at low temperature and high pressure, while the disproportionation process giving C(6)H(5)O + NO via C(6)H(5)ONO becomes competitive at low pressure and dominant at temperatures above 1000 K. 相似文献
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Polyols, a typical type of alcohol containing multiple hydroxyl groups, are being regarded as a new generation of a green energy platform. In this paper, the decomposition mechanisms for three polyol molecules, i.e., 1,2-propanediol, 1,3-propanediol, and glycerol, have been investigated by quantum chemistry calculations. The potential energy surfaces of propanediols and glycerol have been built by the QCISD(T) and CBS-QB3 methods, respectively. For the three molecules studied, the H(2)O-elimination and C-C bond dissociation reactions show great importance among all of the unimolecular decomposition channels. Rate constant calculations further demonstrate that the H(2)O-elimination reactions are predominant at low temperature and pressure, whereas the direct C-C bond dissociation reactions prevail at high temperature and pressure. The temperature and pressure dependence of calculated rate constants was demonstrated by the fitted Arrhenius equations. This work aims to better understand the thermal decomposition process of polyols and provide useful thermochemical and kinetic data for kinetic modeling of polyols-derived fuel combustion. 相似文献
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Shang‐Ying Wu Yun‐Min Lee Jong‐Shinn Wu Ming‐Chang Lin 《International journal of quantum chemistry》2014,114(4):278-288
For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat‐CVD) processes using small silanes as precursors, disilanyl radical (Si2H5) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a‐Si:H film growth on large‐area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si2H5 producing smaller silicon hydrides including SiH, SiH2, SiH3, and Si2H4, and the related reverse reactions involving these species by using ab initio molecular‐orbital calculations. The results show that the lowest energy path is the production of SiH + SiH4 that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si2H5. Additionally, the dissociation energies for breaking the Si? Si and H? SiH2 bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH2, HSiSiH2, and Si2H4(C2h) at 0 K by using the isodesmic reactions, such as 2HSiSiH2 + 1C2H6→1Si2H6 + 2HCCH2 and 1Si2H4(C2h) + 1C2H6 → 1Si2H6 + 1C2H4. The results of SiH (87.2 kcal/mol), SiH2 (64.9 kcal/mol), HSiSiH2 (98.0 kcal/mol), and Si2H4 (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si2H5 and the related bimolecular reverse reactions have been predicted and tabulated for different T, P‐conditions with variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH + SiH4 product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH2 + SiH3, HSiSiH2 + H2, and Si2H4(C2h) + H under T, P‐conditions typically used in PECVD and Cat‐CVD. © 2013 Wiley Periodicals, Inc. 相似文献
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Sirjean B Glaude PA Ruiz-Lopèz MF Fournet R 《The journal of physical chemistry. A》2008,112(46):11598-11610
Whereas many studies have been reported on the reactions of aliphatic hydrocarbons, the chemistry of cyclic hydrocarbons has not been explored extensively. In the present work, a theoretical study of the gas-phase unimolecular decomposition of cyclic alkyl radicals was performed by means of quantum chemical calculations at the CBS-QB3 level of theory. Energy barriers and high-pressure-limit rate constants were calculated systematically. Thermochemical data were obtained from isodesmic reactions, and the contribution of hindered rotors was taken into account. Classical transition state theory was used to calculate rate constants. The effect of tunneling was taken into account in the case of CH bond breaking. Three-parameter Arrhenius expressions were derived in the temperature range of 500-2000 K at atmospheric pressure, and the CC and CH bond breaking reactions were studied for cyclic alkyl radicals with a ring size ranging from three to seven carbon atoms, with and without a lateral alkyl chain. For the ring-opening reactions, the results clearly show an increase of the activation energy as the pi bond is being formed in the ring (endo ring opening) in contrast to the cases in which the pi bond is formed on the side chain (exo ring opening). These results are supported by analyses of the electronic charge density that were performed with Atoms in Molecules (AIM) theory. For all cycloalkyl radicals considered, CH bond breaking exhibits larger activation energies than CC bond breaking, except for cyclopentyl for which the ring-opening and H-loss reactions are competitive over the range of temperatures studied. The theoretical results compare rather well with the experimental data available in the literature. Evans-Polanyi correlations for CC and CH beta-scissions in alkyl and cycloalkyl free radicals were derived. The results highlight two different types of behavior depending on the strain energy in the reactant. 相似文献
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Theoretical study of the unimolecular decomposition mechanisms of energetic TNAD and TNAZ explosives
Min‐Hsien Liu Cheng Chen Yaw‐Shun Hong 《International journal of quantum chemistry》2005,102(4):398-408
Calculation methods based on hybrid Density Functional Theory (DFT) with the basis sets of the B3LYP/6‐31+G(d)//B3LYP/4‐31G(d) method and the differential overlap (INDO) program were used to derive reasonable decomposition mechanisms of 1,4,5,8‐tetranitro‐1,4,5,8‐tetraazadecalin (TNAD) and 1,3,3‐trinitroazetidine (TNAZ) explosives. All possible decomposition species and transition states, including intermediates and products, were identified and their corresponding enthalpy of formation and Gibbs free energy of formation were obtained using polyparametric modification equations. INDO bond energy calculation results reveal the weakest bonding site for reference and determine where cleavage can occur easily. This work is concerned mainly with eliminating HONO (cis or trans form). The activation energy for trans‐form HONO elimination is lower than that of cis‐form HONO elimination in the initial steps of both TNAD and TNAZ decomposition, being 18.5 kJ/mol and 33.3 kJ/mol, respectively. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
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The unimolecular reactions of ammonia oxide H3NO, isomerization and dehydrogenation, are investigated by ab initio MO calculations with the 4-31G basis set. The geometries and energies of the reactant, transition states and products have been determined on the singlet potential energy surface. The reaction ergodography along the intrinsic reaction coordinate (IRC) for the two reactions have been performed. The vibrational frequency correlation diagram of the two reactions are analyzed along the IRC. 相似文献