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应用量子化学从头计算和密度泛函理论(DFT)对HO2+C2H2反应体系的反应机理进行了研究.在B3LYP/6-311G**和CCSD(T)/6-311G**水平上计算了HO2+ C2H2反应的二重态反应势能面.计算结果表明,主要反应方式为自由基HO2的H原子和C2H2分子中的C原子结合,经过一系列异构化,最后分解得到主要产物P1 (CH2O+ HCO).此反应是放热反应,化学反应热为-321.99 kJ·mol-1.次要产物为P2 (CO2 +CH3),也是放热反应. 相似文献
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本文采用UCCSD(T)/aug-cc-pVTZ方法研究了H NH3反应势能面,获得了夺氢反应和交换反应过渡态的的几何结构和振动频率。夺氢反应的过渡态具有Cs对称性,其能垒为61.92 kJ/mol。交换反应的过渡态具有C3v对称性,其能垒为39.69 kJ/mol。H NH3发生形成Td对称性的反应中间体NH4里德堡自由基。与夺氢反应相比,交换反应具有更低的反应能垒,并且NH4自由基在反应中可形成长寿命的共振态,和夺氢反应形成竞争关系,因此在H NH3反应的量子动力学研究中必须同时考虑这两类反应。本文还采用更大的基组aug-cc-pVQZ和aug-cc-pV5Z研究了势能面对基组的收敛行为。 相似文献
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The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391–432°K: The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec?1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M?1· sec?1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined: When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396–442°K: A review of literature data produced k7a = 109.8±0.5M?1·sec?1, giving log k12(M?1·sec?1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments. 相似文献
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We report variational transition‐state theory calculations for the OH + O3→ HO2 + O2 reaction based on the recently reported double many‐body expansion potential energy surface for ground‐state HO4 [Chem Phys Lett 2000, 331, 474]. The barrier height of 1.884 kcal mol?1 is comparable to the value of 1.77–2.0 kcal mol?1 suggested by experimental measurements, both much smaller than the value of 2.16–5.11 kcal mol?1 predicted by previous ab initio calculations. The calculated rate constant shows good agreement with available experimental results and a previous theoretical dynamics prediction, thus implying that the previous ab initio calculations will significantly underestimate the rate constant. Variational and tunneling effects are found to be negligible over the temperature range 100–2000 K. The O1? O2 bond is shown to be spectator like during the reactive process, which confirms a previous theoretical dynamics prediction. © 2007 Wiley Periodicals, Inc. 39: 148–153, 2007 相似文献
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Qiang WANG Zheng Ting CAI Da Cheng FENG 《中国化学快报》2006,17(2):281-284
Many reactions with fluorine atoms have the important applications in the areas of theatmosphere and the chemical lasers, such as the reaction of fluorine atoms with methane. F( 2 P) CH 4 (X1A1)→HF(X1 Σ ) CH 3 (X 2 A′′2) ?H0300k=-32.3 kcal mol ?1 It… 相似文献
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Michael J. Kurylo Jennifer L. Murphy Geoffrey S. Haller Kenneth D. Cornett 《国际化学动力学杂志》1982,14(10):1149-1161
The flash photolysis resonance fluorescence technique has been used to measure the rate constant for the reaction over the temperature range of 250–370 K. The present results are in excellent agreement with three very recent studies, and the combined data set can been used to derive the expression similar to that currently used in atmospheric modeling applications. A summary of our computer simulation of this reaction system is presented. The results of the computations indicate the absence of secondary reaction complications in the present work while revealing significant problems in the earlier (pre-1980) studies of the title reaction. 相似文献
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The ability to use calculated OH frequencies to assign experimentally observed peaks in hydrogen bonded systems hinges on the accuracy of the calculation. Here we test the ability of several commonly employed model chemistries—HF, MP2, and several density functionals paired with the 6‐31+G(d) and 6‐311++G(d,p) basis sets—to calculate the interaction energy (De) and shift in OH stretch fundamental frequency on dimerization (δ(ν)) for the H2O → H2O, CH3OH → H2O, and H2O → CH3OH dimers (where for X → Y, X is the hydrogen bond donor and Y the acceptor). We quantify the error in De and δ(ν) by comparison to experiment and high level calculation and, using a simple model, evaluate how error in De propagates to δ(ν). We find that B3LYP and MPWB1K perform best of the density functional methods studied, that their accuracy in calculating δ(ν) is ≈ 30–50 cm?1 and that correcting for error in De does little to heighten agreement between the calculated and experimental δ(ν). Accuracy of calculated δ(ν) is also shown to vary as a function of hydrogen bond donor: while the PBE and TPSS functionals perform best in the calculation of δ(ν) for the CH3OH → H2O dimer their performance is relatively poor in describing H2O → H2O and H2O → CH3OH. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
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This paper has improved Hickman's nonadiabatic collision model by substituting Hickman's constant velocity classical straight line trajectory approximation with the solution of motion equation mR=?dV(R)/dR, and has calculated the cross sections of ion-pair formation Cs+O2→Cs++O?2 with the improved nonadiabatic collision model (INCM). A comparison of our results with other theoretical and experimental results has been made. 相似文献
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The dynamics of the NH + H→N+H2 reaction has been investigated by means of the 3D quasiclassical trajectory approach by using the LEPS potential energy surface.The calculated rate coefficient is in good agreement with the experimental value.The reaction was found to occur via a direct channel.The product H2 has a cold excitation of rotational state,but has a reverse distribution of the vibrational state with a peak at v=1.Based on the potential energy surface and the trajectory analysis,the reaction mechanism has been explained successfully. 相似文献
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Guang‐Tao Yu Xu‐Ri Huang Yi‐Hong Ding Wei Chen Chia‐Chung Sun 《International journal of quantum chemistry》2007,107(5):1181-1193
The structures, spectroscopies, and stabilities of the doublet Si2NO radical are explored at the density functional theory (DFT) and ab initio levels. Seventeen isomers are located, connected by 26 interconversion transition states. At the CCSD(T)/6‐311+G(2df)//QCISD/6‐311G(d)+ZPVE level, three low‐lying isomers are predicted, that is, one bent species SiNSiO 3 (5.1 kcal/mol) containing the important Si?N triple bonding and two four‐membered ring isomers including cyclic cSiNSiO 1 (0.0) with Si? Si cross‐bonding with C2v symmetry and puckered cSiNSiO 1′ (11.9) with divalent carbene character. Three low‐lying isomers 1, 1′, and 3 have reasonable kinetic stabilities and might be observable either experimentally or astrophysically. The possible formation strategies of 1, 1′, and 3 in laboratory and in space are discussed in detail. The calculated vibrational frequencies and possible formation processes of 3 are consistent with recent experimental observations. In light of the fact that no cyclic nitrogen‐containing species have been detected in space, two cyclic isomers 1 and 1′ could be promising candidates. Furthermore, the bonding nature of three isomers 1, 1′, and 3 is analyzed. The calculated results are also compared with those of the analogue C2NO radical. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
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Calculations for the cumulative reaction probability N(E) (for J=0) and the thermal rate constant k(T) of the H+CH(4)-->H(2)+CH(3) reaction are presented. Accurate electronic structure calculations and a converged Shepard-interpolation approach are used to construct a potential energy surface which is specifically designed to allow the precise calculation of k(T) and N(E). Accurate quantum dynamics calculations employing flux correlation functions and multiconfigurational time-dependent Hartree wave packet propagation compute N(E) and k(T) based on this potential energy surface. The present work describes in detail the various convergence test performed to investigate the accuracy of the calculations at each step. These tests demonstrate the predictive power of the present calculations. In addition, approximate approaches for reaction rate calculations are discussed. A quite accurate approximation can be obtained from a potential energy surface which includes only interpolation points on the minimum energy path. 相似文献
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A flash photolysis system has been used to study the rate of reaction (1), OH + CH4 → CH3 + H2O, using time-resolved resonance absorption to monitor OH. The temperature was varied between 300 and 900°K. It is found that the Arrhenius plot of k1 is strongly curved and k1 (T) can best be represented by the expression The apparent Arrhenius activation energy changes from 15±1 kJ/mole at 300°K to 32±2 kJ/mole at 1000°K. On either side of our temperature range, both absolute rates and their temperature dependence are in good agreement with the results from most previous investigations. 相似文献
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A three-dimensional potential energy surface for the 2A′ ground state of the system (Ne? H2)+ (2Σ+ in collinear geometry) has been calculated at SCF and CEPA levels. This surface describes the abstraction reaction which is endoergic by 0.57 eV (ΔH00) and has been studied recently by different experimental groups at low collision energies. Our CEPA calculations yield an endoergicity of 0.55 eV (ΔH00). The 2A′ surface has a minimum at collinear geometry with RNe—H = 2.29 a0 and RH? H = 2.08 a0 and a well depth of 0.49 eV relative to Ne + H+2. The effects of electron correlation on the shape of the surface and on the well depth are discussed. An analytic fit of the collinear part of the surface has been constructed based on Simon's proposal of using polynomials in the coordinates (R? Re)/R instead of (R? Re). The fitted potential is used for quantum mechanical scattering calculations with the finite element method (FEM ). Preliminary results for reaction probabilities for H+2 in different vibrationally excited states are given and compared to the experimental results. 相似文献
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Jian‐Chao Song Hui‐Ling Liu Zhong‐Jun Zhou Xu‐Ri Huang 《International journal of quantum chemistry》2012,112(6):1654-1666
An in‐depth theoretical study is carried out at the B3LYP/6‐311G(d,p), M062X/aug‐cc‐pVDZ and CCSD(T)/6‐311++G(3df,2dp) (single‐point) levels as an attempt to explore the mechanism of the little‐understood ion–molecule reaction between NH+ and CH2O. Various possible reaction pathways are taken into account. It is shown that six dissociation products, including P 1 (2N + CH2OH+), P 2 (4N + CH2OH+), P 3 (3NH + CH2O+), P 4 (NH2 + HCO+), P 5 (NH + CO), and P 9 (H + CONH) are all accessible both kinetically and thermodynamically. Among these products, P 4 is the most competitive product with predominant abundance, and the second most feasible product is P 3 , followed by P 2 and P 1 . The remaining products, P 5 and P 9 , may have negligible yield under room temperature condition. As the intermediates and transition states involved in the NH+ + CH 2 O reaction all stay below the reactant, the title reaction is expected to be rapid, which is consistent with the measured large rate constant in experiment. The present study will enrich our knowledge of the chemistry of NH+. Furthermore, our calculated result is compared with the previous experimental research, and, meanwhile, it provides a useful guide for understanding analogous reaction, NH+ with CH2NH. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
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A shock tube study of the reaction NH2 + CH4 → NH3 + CH3 and comparison with transition state theory
Soonho Song David M. Golden Ronald K. Hanson Craig T. Bowman Juan P. Senosiain Charles B. Musgrave Gernot Friedrichs 《国际化学动力学杂志》2003,35(7):304-309
The rate coefficient for NH2 + CH4 → NH3 + CH3 (R1) has been measured in a shock tube in the temperature range 1591–2084 K using FM spectroscopy to monitor NH2 radicals. The measurements are combined with a calculation of the potential energy surface and canonical transition state theory with WKB tunneling to obtain an expression for k1 = 1.47 × 103 T 3.01 e?5001/T(K) cm3 mol?1 s?1 that describes available data in the temperature range 300 –2100 K. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 304–309, 2003 相似文献
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Branko S. Jursic 《International journal of quantum chemistry》1997,62(6):639-644
The reaction energy profile for H2 + OH → H + H2O was computed using HF, MP2, MP4, QCISD, G1, G2, and G2MP2 ab initio methods. In addition, the B3LYP, B3P86, B3PW91, BLYP, BP291, and SVWN density functional theory (DFT) methods were also used. All the ab initio methods, with the exception of the G series, produced much higher activation barriers and heats of reaction than the experimental values. On the other hand, the DFT methods produced negative forward and reverse barriers which were too low, with the exception of the hybrid DFT methods. The G2 ab initio method generated energies which deviated from the experimental values by ∼ 1 kcal/mol and therefore should be considered a very accurate computational method. The hybrid DFT methods produced positive forward reaction barriers with energies that were 2–4 kcal/mol lower than the experimental values. The geometries of the transition state and energies computed by the ab initio and DFT methods were compared. These results suggest that, in the hybrid exchange functional, the portion of the Slater exchange term should be increased. This may be the reason why the computed energies were too low. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 62: 639–644, 1997 相似文献
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The title reaction was studied in a crossed‐beam experiment, in which the ground‐state methyl products were probed using a time‐sliced velocity‐imaging technique. By taking images over the energy range of chemical significance, from the threshold to about 15 kcal mol?1, the reactive excitation function as well as the dependences of product angular distributions and of the energy disposal on initial collision energies were determined. All experimental data are consistent with the picture that the ground‐state reaction of O(3P)+CH4 proceeds via a direct abstraction rebound‐type mechanism with a narrow cone of acceptance. Deeper insights into the underlying mechanism and the key feature of the potential‐energy surface are elucidated by comparing the results with the corresponding observables in the analogous Cl+CH4 reaction. 相似文献