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1.
The rate coefficients for the capture process CH + H(2)→ CH(3) and the reactions CH + H(2)→ CH(2) + H (abstraction), CH + H(2) (exchange) have been calculated in the 200-800 K temperature range, using the quasiclassical trajectory (QCT) method and the most recent global potential energy surface. The reactions, which are of interest in combustion and in astrochemistry, proceed via the formation of long-lived CH(3) collision complexes, and the three H atoms become equivalent. QCT rate coefficients for capture are in quite good agreement with experiments. However, an important zero point energy (ZPE) leakage problem occurs in the QCT calculations for the abstraction, exchange and inelastic exit channels. To account for this issue, a pragmatic but accurate approach has been applied, leading to a good agreement with experimental abstraction rate coefficients. Exchange rate coefficients have also been calculated using this approach. Finally, calculations employing QCT capture/phase space theory (PST) models have been carried out, leading to similar values for the abstraction rate coefficients as the QCT and previous quantum mechanical capture/PST methods. This suggests that QCT capture/PST models are a good alternative to the QCT method for this and similar systems. 相似文献
2.
The mode selectivity of the H+CH3D→H2+CH2D reaction was studied using a recently developed ten-dimensional time-dependent wave packet method.The reac-tion dynam... 相似文献
3.
A new full-dimensional potential energy surface for the title reaction has been constructed using the modified Shepard interpolation scheme. Energies and derivatives were calculated using the UCCSD(T) method with aug-cc-pVTZ and 6-311++G(3df,2pd) basis sets, respectively. A total number of 30,000 data points were selected from a huge number of molecular configurations sampled by trajectory method. Quantum dynamical calculations showed that the potential energy surface is well converged for the number of data points for collision energy up to 2.5 eV. Total reaction probabilities and integral cross sections were calculated on the present surface, as well as on the ZBB3 and EG-2008 surfaces for the title reaction. Satisfactory agreements were achieved between the present and the ZBB3 potential energy surfaces, indicating we are approaching the final stage to obtain a global potential energy surface of quantitative accuracy for this benchmark polyatomic system. Our calculations also showed that the EG-2008 surface is less accurate than the present and ZBB3 surfaces, particularly in high energy region. 相似文献
4.
Suleimanov YV Collepardo-Guevara R Manolopoulos DE 《The Journal of chemical physics》2011,134(4):044131
In a recent paper, we have developed an efficient implementation of the ring polymer molecular dynamics (RPMD) method for calculating bimolecular chemical reaction rates in the gas phase, and illustrated it with applications to some benchmark atom-diatom reactions. In this paper, we show that the same methodology can readily be used to treat more complex polyatomic reactions in their full dimensionality, such as the hydrogen abstraction reaction from methane, H + CH(4) → H(2) + CH(3). The present calculations were carried out using a modified and recalibrated version of the Jordan-Gilbert potential energy surface. The thermal rate coefficients obtained between 200 and 2000 K are presented and compared with previous results for the same potential energy surface. Throughout the temperature range that is available for comparison, the RPMD approximation gives better agreement with accurate quantum mechanical (multiconfigurational time-dependent Hartree) calculations than do either the centroid density version of quantum transition state theory (QTST) or the quantum instanton (QI) model. The RPMD rate coefficients are within a factor of 2 of the exact quantum mechanical rate coefficients at temperatures in the deep tunneling regime. These results indicate that our previous assessment of the accuracy of the RPMD approximation for atom-diatom reactions remains valid for more complex polyatomic reactions. They also suggest that the sensitivity of the QTST and QI rate coefficients to the choice of the transition state dividing surface becomes more of an issue as the dimensionality of the reaction increases. 相似文献
5.
H+CH3NO2H2+CH2NO2反应途径和变分速率常数计算研究 总被引:1,自引:0,他引:1
采用MP2(FULL)/6-311G**从头算方法, 优化了H+CH3NO2H2+ CH2NO2反应的过渡态结构, 得出该反应的正逆反应的活化位垒分别是82.73和57.14 kJ*mol-1. 沿IRC分析指出该反应是一个H-H键生成和C-H键断裂的协同反应, 而且在反应途径上存在一个引导反应进行的振动模式, 这一反应模式引导反应进行的区间在-0.7~0.2( amu)1/2*a0之间; 在1 000~1 400 K温度范围内, 运用变分过渡态理论(CVT), 计算了该反应的速率常数, 计算结果与实验相一致. 相似文献
6.
We report a high-quality, ab initio, full-dimensional global potential energy surface (PES) for the Cl((2)P, (2)P(3/2)) + CH(4) reaction, which describes both the abstraction (HCl + CH(3)) and substitution (H + CH(3)Cl) channels. The analytical PES is a least-squares fit, using a basis of permutationally invariant polynomials, to roughly 16,000 ab initio energy points, obtained by an efficient composite method, including counterpoise and spin-orbit corrections for the entrance channel. This composite method is shown to provide accuracy almost equal to all-electron CCSD(T)/aug-cc-pCVQZ results, but at much lower computational cost. Details of the PES, as well as additional high-level benchmark characterization of structures and energetics are reported. The PES has classical barrier heights of 2650 and 15,060 cm(-1) (relative to Cl((2)P(3/2)) + CH(4)(eq)), respectively, for the abstraction and substitution reactions, in good agreement with the corresponding new computed benchmark values, 2670 and 14,720 cm(-1). The PES also accurately describes the potential wells in the entrance and exit channels for the abstraction reaction. Quasiclassical trajectory calculations using the PES show that (a) the inclusion of the spin-orbit corrections in the PES decreases the cross sections by a factor of 1.5-2.5 at low collision energies (E(coll)); (b) at E(coll) ≈ 13,000 cm(-1) the substitution channel opens and the H/HCl ratio increases rapidly with E(coll); (c) the maximum impact parameter (b(max)) for the abstraction reaction is ~6 bohr; whereas b(max) is only ~2 bohr for the substitution; (d) the HCl and CH(3) products are mainly in the vibrational ground state even at very high E(coll); and (e) the HCl rotational distributions are cold, in excellent agreement with experiment at E(coll) = 1280 cm(-1). 相似文献
7.
8.
Michael J. Polce Chrys Wesdemiotis 《Journal of the American Society for Mass Spectrometry》1996,7(6):573-589
Metastable ion decompositions, collision-activated dissociation (CAD), and neutralization-reionization mass spectrometry are utilized to study the unimolecular chemistry of distonic ion ·CH2CH2CH?OH (2+·) and its enol-keto tautomers CH3CH=CHOH?· (1 +·) and CH3CH2CH=O +· (3+·). The major fragmentation of metastable 1+·–3+· is H· loss to yield the propanoyl cation, CH3CH2C≡O+. This reaction remains dominant upon collisional activation, although now some isomeric CH2=CH-CH+ OH is coproduced from all three precursors. The CAD and neutralization-reionization (+NR+) spectra of keto ion 3 +· are substantially different from those of tautomers 2+· and 1+·. Hence, 3+· without sufficient energy for decomposition (i. e. , “stable” 3+·) does not isomerize to the ther-modynamically more stable ions 2+· or 1+·, and the 1,4-H rearrangement H-CH2CH2CH=O+·(3 +·) → CH2CH2CH+ O-H (2 +·) must require an appreciable critical energy. Although the fragment ion abundances in the + NR + (and CAD) spectra of 1 +· and 2 +· are similar, the relative and absolute intensities of the survivor ions (recovered C3H6O+· ions in the +NR+ spectra) are markedly distinct and independent of the internal energy of 1 +· and 2 +·. Furthermore, 1 +· and 2 +· show different MI spectra. Based on these data, distonic ion 2 +· does not spontaneously rearrange to enol ion 1 +· (which is the most stable C3H6O+· of CCCO connectivity) and, therefore, is separated from it by an appreciable barrier. In contrast, the molecular ions of cyclopropanol (4 +·) and allyl alcohol (5 +·) isomerize readily to 2 +·, via ring opening and 1,2-H? shift, respectively. The sample found to generate the purest 2 +· is α-hydroxy-γ-butyrolactone. Several other precursors that would yield 2 +· by a least-motion reaction cogenerate detectable quantities of enol ion 1 +·, or the enol ion of acetone (CH2=C(CH3)OH+·, 6 +·), or methyl vinyl ether ion (CH3OCH=CH 2 +· , 7 +·). Ion 6 +· is coproduced from samples that contain the —CH2—CH(OH)—CH2— substructure, whereas 7 +· is coproduced from compounds with methoxy substituents. Compared to CAD, metastable ion characteristics combined with neutralization-reionization allow for a superior differentiation of the ions studied. 相似文献
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用变分过渡态理论对CH3SiH3与H的抽提反应进行了理论研究;利用从头算计算了反应体系的构型、振动频率和能量等信息;计算了温度在298 ~1700K内反应的速率常数和穿透系数。结果表明,在室温下,变分对于此反应影响较大,隧道效应特别明显,计算得到的速率常数和实验值符合得很好。 相似文献
11.
《Radiation Physics and Chemistry》1999,53(1):37-46
The mechanism and kinetics of energy transfer from Xe(6s[3/2]1) resonance state (E=8.44 eV) to selected hydrocarbon molecules have been investigated by XeCl(B–X) (λmax=308 nm) fluorescence intensity measurements at stationary conditions in Xe–CCl4–M systems. Steady-state analysis of the fluorescence intensity dependence on the xenon and M pressure at constant CCl4 concentration shows that these process occur in the two- and three-body reactions: Xe(6s[3/2]10)+M→products, Xe(6s[3/2]10+M+Xe→products. The two- and three-body rate constants for these reactions have been found (see Table 1Table 1. Experimental parameters of Eq. (8)found by least square method in Xe–CCl4–C2H2 and Xe–CCl4–C2H4 systems for chosen xenon pressures in the range 25–150 Torr. Linear correlation coefficients (R) are also shown
P(Xe) (Torr) | C2H4 | C2H2 | ||||
---|---|---|---|---|---|---|
Empty Cell | a | b×1016 cm3/molec. | R | a | b×1016 cm3/molec. | R |
25 | 0.92 | 3.26 | 0.98 | 1.00 | 2.78 | 0.95 |
40 | 0.86 | 3.29 | 0.97 | 1.00 | 2.91 | 0.98 |
50 | 0.87 | 3.33 | 0.97 | 0.99 | 3.05 | 0.98 |
60 | 0.85 | 3.33 | 0.97 | 1.02 | 2.99 | 0.98 |
75 | 0.86 | 3.39 | 0.97 | 1.03 | 2.95 | 0.98 |
90 | 0.92 | 3.30 | 0.97 | 1.03 | 2.85 | 0.98 |
100 | 0.92 | 3.21 | 0.98 | 1.0 | 2.77 | 0.98 |
110 | 0.88 | 3.19 | 0.96 | 1.02 | 2.71 | 0.99 |
125 | 0.86 | 3.12 | 0.95 | — | — | — |
140 | 0.92 | 2.90 | 0.95 | — | — | — |
150 | 0.95 | 2.77 | 0.94 | — | — | — |