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1.
The reaction mechanism of the Y+ cation with CH3CHO has been investigated with a DFT approach. All the stationary points are determined at the UB3LYP/ECP/6-311++G** level of the theory. Both ground and excited state potential energy surfaces are investigated in detail. The present results show that the title reaction start with the formation of a CH3CHO-metal complex followed by C-C, aldehyde C-H, methyl C-H and C-O activation. These reactions can lead to four different products (Y+CH4 + CO, Y+CO + CH4, Y+COCH2 + H2 and Y+O + C2H4). The minimum energy reaction path is found to involve the spin inversion in the different reaction steps, this potential energy curve-crossing dramatically affects reaction exothermic. The present results may be helpful in understanding the mechanism of the title reaction and further experimental investigation of the reaction.  相似文献   

2.
The thermal ion‐molecule reactions NiX++CH4→Ni(CH3)++HX (X=H, CH3, OH, F) have been studied by mass spectrometric methods, and the experimental data are complemented by density functional theory (DFT)‐based computations. With regard to mechanistic aspects, a rather coherent picture emerges such that, for none of the systems studied, oxidative addition/reductive elimination pathways are involved. Rather, the energetically most favored variant corresponds to a σ‐complex‐assisted metathesis (σ‐CAM). For X=H and CH3, the ligand exchange follows a ‘two‐state reactivity (TSR)’ scenario such that, in the course of the thermal reaction, a twofold spin inversion, i.e., triplet→singlet→triplet, is involved. This TSR feature bypasses the energetically high‐lying transition state of the adiabatic ground‐state triplet surface. In contrast, for X=F, the exothermic ligand exchange proceeds adiabatically on the triplet ground state, and some arguments are proposed to account for the different behavior of NiX+/Ni(CH3)+ (X=H, CH3) vs. NiF+. While the couple Ni(OH)+/CH4 does not undergo a thermal ligand switch, the DFT computations suggest a potential‐energy surface that is mechanistically comparable to the NiF+/CH4 system. Obviously, the ligands X act as a mechanistic distributor to switch between single vs. two‐state reactivity patterns.  相似文献   

3.
We study dynamics of the CH3 + OH reaction over the temperature range of 300–2500 K using a quasiclassical method for the potential energy composed of explicit forms of short‐range and long‐range interactions. The explicit potential energy used in the study gives minimum energy paths on potential energy surfaces showing barrier heights, channel energies, and van der Waals well, which are consistent with ab initio calculations. Approximately, 20% of CH3 + OH collisions undergo OH dissociation in a direct‐mode mechanism on a subpicosecond scale (<50 fs) with the rate coefficient as high as ~10?10 cm3 molecule?1 s?1. Less than 10% leads to the formation of excited intermediates CH3OH? with excess vibrational energies in CO and OH bonds. CH3OH? stabilizes to CH3OH, redissociates back to reactants, or forms one of various products after intramolecular energy redistribution via bond dissociation and formation on the time scale of 50–200 fs. The principal product is 1CH2 (k being ~10?11), whereas ks for CH2OH, CH2O, and CH3O are ~10?12. The minor products are HCOH and CH4 (k~10?13). The total rate coefficient for CH3 + OH → CH3OH? → products is ~10?11 and is weakly dependent on temperature. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 455–466, 2011  相似文献   

4.
The dissociation and isomerization reaction mechanism on the ground‐state potential energy surface for CH2ClI are investigated by ab initio calculations. It is found that the isomer iso‐CH2I‐Cl can be produced from either the recombination of the photodissociation fragments or the isomerization reaction of CH2ClI, rather than from isomerization reaction of iso‐CH2Cl‐I. Further explanations of experimental results are also presented. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004  相似文献   

5.
This paper reports on the gas‐phase radical–radical dynamics of the reaction of ground‐state atomic oxygen [O(3P), from the photodissociation of NO2] with secondary isopropyl radicals [(CH3)2CH, from the supersonic flash pyrolysis of isopropyl bromide]. The major reaction channel, O(3P)+(CH3)2CH→C3H6 (propene)+OH, is examined by high‐resolution laser‐induced fluorescence spectroscopy in crossed‐beam configuration. Population analysis shows bimodal nascent rotational distributions of OH (X2Π) products with low‐ and high‐N′′ components in a ratio of 1.25:1. No significant spin–orbit or Λ‐doublet propensities are exhibited in the ground vibrational state. Ab initio computations at the CBS‐QB3 theory level and comparison with prior theory show that the statistical method is not suitable for describing the main reaction channel at the molecular level. Two competing mechanisms are predicted to exist on the lowest doublet potential‐energy surface: direct abstraction, giving the dominant low‐N′′ components, and formation of short‐lived addition complexes that result in hot rotational distributions, giving the high‐N′′ components. The observed competing mechanisms contrast with previous bulk kinetic experiments conducted in a fast‐flow system with photoionization mass spectrometry, which suggested a single abstraction pathway. In addition, comparison of the reactions of O(3P) with primary and tertiary hydrocarbon radicals allows molecular‐level discussion of the reactivity and mechanism of the title reaction.  相似文献   

6.
Two mixed‐valent disc‐like hepta‐nuclear compounds of [FeIIFeIII6(tea)6](ClO4)2 ( 1Fe , tea = N(CH2CH2O)33?) and [MnII3MnIII4(nmdea)6(N3)6]·CH3OH ( 2Mn , nmdea = CH3N(CH2CH2O)22?) have been synthesized by the reaction of Fe(ClO4)2·6H2O with triethanolamine (H3tea) for the former and reaction of Mn(ClO4)2·6H2O with diethanolamine (H2nmdea) and NaN3 for the later, respectively. 1Fe has the cationic cluster with a planar [FeIIFeIII6] core consisting of one central FeII and six rim FeIII atoms in hexagonal arrangement. The Fe ions are linked by the oxo‐bridges from the alcohol arms in the manner of edge‐sharing of their coordination octahedra. 2Mn is a neutral cluster with a [MnII3MnIII4] core possessing one central MnII atom surrounded by six rim Mn ions, two MnII and four MnIII. The structure is similar to 1Fe but involves six terminal azido ligands, each coordinate one rim Mn ion. 1Fe showed dominant antiferromagnetic interaction within the cluster and long‐range ordering at 2.7 K. The cluster probably has a ground state of low spin of S = 5/2 or 4/2. The long‐range ordering is weak ferromagnetic, showing small hysteresis with a remnant magnetization of 0.3 Nβ and a coercive field of 40 Oe. Moreover, the isofield of lines 1Fe are far from superposition, indicating the presence of significant zero–field splitting. Ferromagnetic interactions are dominant in 2Mn . An intermediate spin ground state 25/2 is observed at low field. In high field of 50 kOe, the energetically lowest state is given by the ms = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. Despite of the large ground state, no single‐molecule magnet behavior was found above 2 K.  相似文献   

7.
The potential energy surface of O(1D) + CH3CH2Br reaction has been studied using QCISD(T)/6‐311++G(d,p)//MP2/6‐311G(d,p) method. The calculations reveal an insertion‐elimination reaction mechanism of the title reaction. The insertion process has two possibilities: one is the O(1D) inserting into C? Br bond of CH3CH2Br producing one energy‐rich intermediate CH3CH2OBr and another is the O(1D) inserting into one of the C? H bonds of CH3CH2Br producing two energy‐rich intermediates, IM1 and IM2. The three intermediates subsequently decompose to various products. The calculations of the branching ratios of various products formed though the three intermediates have been carried out using RRKM theory at the collision energies of 0, 5, 10, 15, 20, 25, and 30 kcal/mol. CH3CH2O + Br are the main decomposition products of CH3CH2OBr. CH3COH + HBr and CH2CHOH + HBr are the main decomposition products for IM1; CH2CHOH + HBr are the main decomposition products for IM2. As IM1 is more stable and more likely to form than CH3CH2OBr and IM2, CH3COH + HBr and CH2CHOH + HBr are probably the main products of the O(1D) + CH3CH2Br reaction. Our computational results can give insight into reaction mechanism and provide probable explanations for future experiments. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011  相似文献   

8.
A direct dynamics study was carried out for the multichannel reaction of CH3NHNH2 with OH radical. Two stable Conformers (I, II) of CH3NHNH2 are identified by the rotation of the ? CH3 group. For each conformer, five hydrogen‐abstraction channels are found. The reaction mechanisms of product radicals (CH3NNH2 and CH3NHNH) with OH radical are also investigated theoretically. The electronic structure information on the potential energy surface is obtained at the B3LYP/6‐311G(d,p) level and the energetics along the reaction path is refined by the BMC‐CCSD method. Hydrogen‐bonded complexes are presented at both the reactant and product sides of the five channels, indicating that the reaction may proceed via an indirect mechanism. The influence of the basis set superposition error (BSSE) on the energies of all the complexes is discussed by means of the CBS‐QB3 method. The rate constants of CH3NHNH2 + OH are calculated using canonical variational transition‐state theory with the small‐curvature tunneling correction (CVT/SCT) in the temperature range of 200–1000 K. Slightly negative temperature dependence of rate constant is found in the temperature range from 200 to 345 K. The agreement between the theoretical and experimental results is good. It is shown that for Conformer I, hydrogen‐abstraction from ? NH? position is the primary pathway at low temperature; the hydrogen‐abstraction from ? NH2 is a competitive pathway as the temperature increases. A similar case can be concluded for Conformer II. The overall rate constant is evaluated by considering the weight factors of each conformer from the Boltzmann distribution function, and the three‐term Arrhenius expressions are fitted to be kT = 1.6 × 10?24T4.03exp (1411.5/T) cm3 molecule?1 s?1 between 200–1000 K. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009  相似文献   

9.
The rate constants and H/D kinetic isotope effect for hydrogen abstraction reactions involving isotopomers of methyl formate by methyl radical are computed employing methods of the variational transition state theory (VTST) with multidimensional tunneling corrections. The energy paths were built with a dual-level method using the moller plesset second-order perturbation theory (MP2) method as the low-level and complete basis set (CBS) extrapolation as the high-level energy method. Benchmark calculations with the CBSD-T approach give an enthalpy of reaction at 0 K for R1 (−4.5 kcal/mol) and R2 (−4.2 kcal/mol) which are in good agreement with the experiment, that is, −4.0 and − 4.8 kcal/mol. For the reactional paths involving the isotopomers CH3 + CH3OCOH → CH4 + CH3OCO and CH3 + CH3OCOD → CH3D + CH3OCO, the value of kH/kD (T = 455 K) using the canonical VTST/small-curvature tunneling approximation method is 6.7 in close agreement with experimental value (6.2). © 2019 Wiley Periodicals, Inc.  相似文献   

10.
The mechanism of the reaction of ketene with methyl radical has been studied by ab initio CCSD(T)‐F12/cc‐pVQZ‐f12//B2PLYPD3/6‐311G** calculations of the potential energy surface. Temperature‐ and pressure‐dependent reaction rate constants have been computed using the Rice–Ramsperger–Kassel–Marcus (RRKM)–Master Equation and transition state theory methods. Three main channels have been shown to dominate the reaction; the formation of the collisionally stabilized CH3COCH2 radical and the production of the C2H5 + CO and HCCO + CH4 bimolecular products. Relative contributions of the CH3COCH2, C2H5 + CO, and HCCO + CH4 channels strongly depend on the reaction conditions; the formation of thermalized CH3COCH2 is favored at low temperatures and high pressures, HCCO + CH4 is dominant at high temperatures, whereas the yield of C2H5 + CO peaks at intermediate temperatures around 1000 K. The C2H5 + CO channel is favored by a decrease in pressure but remains the second most important reaction pathway after HCCO + CH4 under typical flame conditions. The calculated rate constants at different pressures are proposed for kinetic modeling of ketene reactions in combustion in the form of modified Arrhenius expressions. Only rate constant to form CH3COCH2 depends on pressure, whereas those to produce C2H5 + CO and HCCO + CH4 appeared to be pressure independent.  相似文献   

11.
Rate constants for the gas‐phase reactions of CH3OCH2CF3 (k1), CH3OCH3 (k2), CH3OCH2CH3 (k3), and CH3CH2OCH2CH3 (k4) with NO3 radicals were determined by means of a relative rate method at 298 K. NO3 radicals were prepared by thermal decomposition of N2O5 in a 700–750 Torr N2O5/NO2/NO3/air gas mixture in a 1‐m3 temperature‐controlled chamber. The measured rate constants at 298 K were k1 = (5.3 ± 0.9) × 10?18, k2 = (1.07 ± 0.10) × 10?16, k3 = (7.81 ± 0.36) × 10?16, and k4 = (2.80 ± 0.10) × 10?15 cm3 molecule?1 s?1. Potential energy surfaces for the NO3 radical reactions were computationally explored, and the rate constants of k1k5 were calculated according to the transition state theory. The calculated values of rate constants k1k4 were in reasonable agreement with the experimentally determined values. The calculated value of k5 was compared with the estimate (k5 < 5.3 × 10?21 cm3 molecule?1 s?1) derived from the correlation between the rate constants for reactions with NO3 radicals (k1k4) and the corresponding rate constants for reactions with OH radicals. We estimated the tropospheric lifetimes of CH3OCH2CF3 and CHF2CF2OCH2CF3 to be 240 and >2.4 × 105 years, respectively, with respect to reaction with NO3 radicals. The tropospheric lifetimes of these compounds are much shorter with respect to the OH reaction. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 490–497, 2009  相似文献   

12.
13.
The gas phase association of CH3 with the HAr2 cluster to form a vibrationally/rotationally excited CH 4 * molecule is used as a model to study microscopic solvation dynamics. A potential energy surface for the reactive system is constructed from a previously fitted H + CH3 ab initio potential and 12-6 Lennard-Jones Ar-Ar, Ar-C, and Ar-H potentials. Classical trajectory calculations performed with the chemical dynamics computer program VENUS are used to investigate the CH3 + HAr2 → CH 4 * + Ar2 reaction dynamics. Reaction is dominated by a mechanism in which the CH3 “strips” the H-atom from HAr2 during large impact parameter collisions. For a large initial relative translational energy the CH3 + HAr2 → CH 4 * + Ar2 cross section is the same as that for H + CH3 association, so that HAr2 acts like a “heavy” H-atom. However, at a low initial relative translational energy, the long-range Ar2—CH3 attractive potential apparently makes the CH3 + HAr2 association cross section larger than that for H + CH3. Partitioning of energy to the CH 4 * and Ar2 products is consistent with a stripping mechanism. The initial and final relative translational energies are nearly identical and the CH 4 * rotational energy is controlled by the initial CH3 rotational energy. The velocity and orbital tilt scattering angles, θ(v i ,v f ) and θ(l i ,l f ), respectively, are consistent with the stripping mechanism. On average only a small amount of the product energy is partitioned to Ar2 vibration/rotation and CH 4 * + Ar2 relative translation.  相似文献   

14.
The multiple‐channel reactions OH + CH3SCH3 → products, CF3 + CH3SCH3 → products, and CH3 + CH3SCH3 → products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6‐31+G(d,p) level, and energetic information is further refined by the MC‐QCISD (single‐point) method. The rate constants for eight reaction channels are calculated by the improved canonical variational transition state theory with small‐curvature tunneling contribution over the temperature range 200–3000 K. The total rate constants are in good agreement with the available experimental data and the three‐parameter expressions k1 = 4.73 × 10?16T1.89 exp(?662.45/T), k2 = 1.02 × 10?32T6.04 exp(933.36/T), k3 = 3.98 × 10?35T6.60 exp(660.58/T) (in unit of cm3 molecule?1 s?1) over the temperature range of 200–3000 K are given. Our calculations indicate that hydrogen abstraction channels are the major channels and the others are minor channels over the whole temperature range. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010  相似文献   

15.
The abstraction of the halogenide ligands in [Re(CH3CN)2Cl4]? should result in a solvent‐only stabilized ReIII complex. The reactions of salts of [Re(CH3CN)2Cl4]? with silver(I) and thallium(I) salts were investigated and the solid‐state structures of cis‐[Re(CH3CN)2Cl4]·CH3CN and cis‐[Re(NHC(OCH3)CH3)2Cl4] are described.  相似文献   

16.
In the course of an extensive investigation aimed at understanding the detailed mechanism of a prototypical polyatomic reaction, several remarkable observations were uncovered. To interpret these findings, we surmise the existence of a reactive resonance in this polyatomic reaction. The concerned system is HO + CH4 → H2O + CH3, of which the partial potential energy surface is constructed by the coupling between vibrational models and reactive coordinates. Then we explain the formation mechanism of the reactive resonance state by the partial potential energy surface. Finally, we estimated the lifetime of the resonance state, and it is about 45fs. The study of the reactive resonance in a polyatomic reaction is more than just an extension from a typical atom + diatom reaction. As shown here, it holds great promise to disentangle the elusive intramolecular vibrational dynamics of the transient collision complex in the critical transition‐state region. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008  相似文献   

17.
The rate coefficients of the gas‐phase reactions CH2OO + CH3COCH3 and CH2OO + CH3CHO have been experimentally determined from 298–500 K and 4–50 Torr using pulsed laser photolysis with multiple‐pass UV absorption at 375 nm, and products were detected using photoionization mass spectrometry at 10.5 eV. The CH2OO + CH3CHO reaction's rate coefficient is ~4 times faster over the temperature 298–500 K range studied here. Both reactions have negative temperature dependence. The T dependence of both reactions was captured in simple Arrhenius expressions: The rate of the reactions of CH2OO with carbonyl compounds at room temperature is two orders of magnitude higher than that reported previously for the reaction with alkenes, but the A factors are of the same order of magnitude. Theoretical analysis of the entrance channel reveals that the inner 1,3‐cycloaddition transition state is rate limiting at normal temperatures. Predicted rate‐coefficients (RCCSD(T)‐F12a/cc‐pVTZ‐F12//B3LYP/MG3S level of theory) in the low‐pressure limit accurately reproduce the experimentally observed temperature dependence. The calculations only qualitatively reproduce the A factors and the relative reactivity between CH3CHO and CH3COCH3. The rate coefficients are weakly pressure dependent, within the uncertainties of the current measurements. The predicted major products are not detectable with our photoionization source, but heavier species yielding ions with masses m/z = 104 and 89 are observed as products from the reaction of CH2OO with CH3COCH3. The yield of m/z = 89 exhibits positive pressure dependence that appears to have already reached a high‐pressure limit by 25 Torr.  相似文献   

18.
By employing time‐resolved Fourier transform infrared emission spectroscopy, the fragments HCl (v=1–3), HBr (v=1), and CO (v=1‐3) are detected in one‐photon dissociation of 2‐bromopropionyl chloride (CH3CHBrCOCl) at 248 nm. Ar gas is added to induce internal conversion and to enhance the fragment yields. The time‐resolved high‐resolution spectra of HCl and CO were analyzed to determine the rovibrational energy deposition of 10.0±0.2 and 7.4±0.6 kcal mol?1, respectively, while the rotational energy in HBr is evaluated to be 0.9±0.1 kcal mol?1. The branching ratio of HCl(v>0)/HBr(v>0) is estimated to be 1:0.53. The bond selectivity of halide formation in the photolysis follows the same trend as the halogen atom elimination. The probability of HCl contribution from a hot Cl reaction with the precursor is negligible according to the measurements of HCl amount by adding an active reagent, Br2, in the system. The HCl elimination channel under Ar addition is verified to be slower by two orders of magnitude than the Cl elimination channel. With the aid of ab initio calculations, the observed fragments are dissociated from the hot ground state CH3CHBrCOCl. A two‐body dissociation channel is favored leading to either HCl+CH3CBrCO or HBr+CH2CHCOCl, in which the CH3CBrCO moiety may further undergo secondary dissociation to release CO.  相似文献   

19.
Experimental and theoretical rate coefficients are determined for the first time for the reaction of 4‐hydroxy‐3‐hexanone (CH3CH2C(O)CH(OH)CH2CH3) with OH radicals as a function of temperature. Experimental studies were carried out using two techniques. Absolute rate coefficients were measured using a cryogenically cooled cell coupled to the pulsed laser photolysis‐laser‐induced fluorescence technique with temperature and pressure ranges of 280‐365 K and 5‐80 Torr, respectively. Relative values of the studied reaction were measured under atmospheric pressure in the range of 298‐354 K by using a simulation chamber coupled to a FT‐IR spectrometer. In addition, the reaction of 4H3H with OH radicals was studied theoretically by using the density functional theory method over the range of 278‐350 K. Results show that H‐atom abstraction occurs more favorably from the C–H bound adjacent to the hydroxyl group with small barrier height. Theoretical rate coefficients are in good agreement with the experimental data. A slight negative temperature dependence was observed in both theoretical and experimental works. Overall, the results are deliberated in terms of structure–reactivity relationship and atmospheric implications.  相似文献   

20.
Complete active space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) calculations with contracted ANO‐RCC basis set were performed for low‐lying electronic states of CH3SS and its cation in Cs symmetry. For the ground state X2A″ of CH3SS, the calculated S‐S stretching mode is in good agreement with experimental reports. The electron transitions of CH3SS+, X1A′ → 11A″, X1A′ → 21A′, and X1A′ → 21A″, are predicted at 1.055, 3.247, and 3.841 eV. Moreover, the calculated adiabatic and vertical ionization potential and adiabatic affinity are in reasonable agreement with the experimental data. The CASSCF/CASPT2 potential energy curves (PECs) were calculated for S2‐loss dissociation from the X2A″, 12A′, and 22A″ states. The electronic states of the CH3 radical and S2 molecule as the dissociation products were carefully determined by checking energies and geometries of the asymptote products. The S2‐loss PEC for CH3SS indicate that S2‐loss dissociation occurs from the X2A″ state leading to CH3 (12A″) + S2 (X3Σ), the 12A′ and 22A″ leading to CH3 (12A″) + S2 (1Δg). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012.  相似文献   

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