CH_3SGN与O_2气相反应机理的理论研究

在G3(MP2)水平上,通过对CH_3S与O_2rcyi2rvylce dm (PES)上关键驻点的能 量计算,共找到4种中间体,9个过渡态,6种产物通道,并对这些气相反应机理进 行了讨论,同时应用TST－RRKM理论对主要反应的速率进行计算。结果表明:CH_3S 与O_2反应在低温下以生成CH_3SOO为主,并与实验结果吻合;在中高温下以消去和 抽提反应为主,分别生成CH_3 + SO_2和CH_2S + HO_2,其它产物较少。     

CH3与NO2的反应

The elementary reaction of the CH3 radical with NO2 was investigated by time-resolved FTIR spectroscopy and quantum chemical calculations. The CH3 radical was produced by laser photolysis of CH3Br or CH3I at 248 nm. Vibrationally excited products OH, HNO and CO2 were observed by the time-resolved spectroscopy for the first time. The formation of another product NO was also verified. According to these observations, the product channels leading to CH3O+NO, CH2NO+OH and HNO+H2CO were identified. The channel of CH3O+NO was the major one. The reaction mechanisms of the above channels were studied by quantum chemical calculations at CCSD(T)/6-311++G(df,p)//MP2/6-311G(d,p) level. The calculated results fit with the experimental observations well.     

Theoretical study on the gas-phase reaction mechanism between palladium monoxide and methane

The gas-phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6-311+G(2d, 2p), SDD level. The major reaction channel leads to the products PdCH(2) + H(2)O, whereas the minor channel results in the products Pd + CH(3)OH, CH(2)OPd + H(2), and PdOH + CH(3). The minimum energy reaction pathway for the formation of main products (PdCH(2) + H(2)O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH(3)PdOH and CH(3)Pd(O)H are the critical intermediates. Furthermore, the rate-determining step is RS-CH(3) PdOH → RS-2-TS1cb → RS-CH(2)Pd(H)OH with the rate constant of k = 1.48 × 10(12) exp(-93,930/RT). For the first C-H bond cleavage, both the activation strain ΔE(≠)(strain) and the stabilizing interaction ΔE(≠)(int) affect the activation energy ΔE(≠), with ΔE(≠)(int) in favor of the direct oxidative insertion. On the other hand, in the PdCH(2) + H(2) O reaction, the main products are Pd + CH(3)OH, and CH(3)PdOH is the energetically preferred intermediate. In the CH(2)OPd + H(2) reaction, the main products are Pd + CH(3)OH with the energetically preferred intermediate H(2)PdOCH(2). In the Pd + CH(3)OH reaction, the main products are CH(2)OPd + H(2), and H(2)PdOCH(2) is the energetically predominant intermediate. The intermediates, PdCH(2), H(2) PdCO, and t-HPdCHO are energetically preferred in the PdC + H(2), PdCO + H(2), and H(2)Pd + CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first-row congener NiO.     

Kinetics of the reactions of CH2Br and CH2I radicals with molecular oxygen at atmospheric temperatures

The kinetics of the reactions of CH2Br and CH2I radicals with O2 have been studied in direct measurements using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals have been homogeneously generated by pulsed laser photolysis of appropriate precursors at 193 or 248 nm. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of O2 being in large excess over radical concentrations. No buffer gas density dependence was observed for the CH2I + O2 reaction in the range 0.2-15 x 10(17) cm(-3) of He at 298 K. In this same density range the CH2Br + O2 reaction was obtained to be in the third-body and fall-off area. Measured bimolecular rate coefficient of the CH2I + O2 reaction is found to depend on temperature as k(CH2I + O2)=(1.39 +/- 0.01)x 10(-12)(T/300 K)(-1.55 +/- 0.06) cm3 s(-1)(220-450 K). Obtained primary products of this reaction are I atom and IO radical and the yield of I-atom is significant. The rate coefficient and temperature dependence of the CH2Br + O2 reaction in the third-body region is k(CH2Br + O2+ He)=(1.2 +/- 0.2)x 10(-30)(T/300 K)(-4.8 +/- 0.3) cm6 s(-1)(241-363 K), which was obtained by fitting the complete data set simultaneously to a Troe expression with the F(cent) value of 0.4. Estimated overall uncertainties in the measured reaction rate coefficients are about +/-25%.     

HAsO~2异构体结构、相对稳定性与体系势能面

在MP2/6-311++G(d,p)和QCISD(T)/6-311++G(3df,2p)(单点)水平下计算得到了包括9个异构体和10个过滤态的HAsO~2体系势能面。在势能面上，异构体cis-HOAsO(E1)的能量是最低的，其次是trans-HOAsO(E2)和HAsO(O)(C~2~V,E3)，能量分别比cis-HOAsO高13.15和192.74kJ/mol。根据体系的势能面，异构体E1，E3及cis-HOOAs(E6),trans-HOOAs(E5)具有一定的动力学稳定性，在实验中应该可以观测到。AsH和O~2反应的第一步产物将会异构化为具有较高动力学稳定性的异构体E3；而OH和AsO反应可直接生成E1。计算结果与HPO~2,HPS~2,HNO~2,HNS~2等价电子相同的分子的势能面进行了比较。     

CBr+O_2反应在二重态势能面上的机理研究(英文)

用UB3LYP/6-311++G(d,p)和QCISD(单点能)的方法考察了CBr+O2反应在二重态势能面上的反应机理。研究发现该反应在高温过程中重要,且有两个产物通道,它们分别是BrCO+O和Br+CO2,其中前者为优势通道。为了弄清溴原子取代对次甲基与氧气反应的机理的影响,我们对CBr+O2反应与CH+O2反应的相似性和差异也作了讨论。结果表明:两反应的第一步都是CX(X=H,Br)自由基与氧气反应生成链状过氧化物XCOO,且溴原子取代对反应的活性、产物通道的数量和产物的形成过程等都有影响。     

OBrO+NO反应机理的量子化学研究

用密度泛函B3LYP/6-311+G^**和高级电子相关偶合簇CCSD(T)/6-311+G^**方法研究了OBrO与NO反应的微观机理.优化得到反应路径上的反应物、过渡态、中间体和产物的几何构型,通过频率振动分析对过渡态和中间体进行了确认.结果表明;该反应是多通道多步骤的放热反应,分别可以在单重态和三重态势能面上进行,OBrO与NO通过加成及加成-消除机理分别形成产物BrONO₂和BrO+NO₂,从能量上看,形成离解产物的通道更容易进行.     

Theoretical study on the reaction mechanism of the methyl radical with nitrogen oxides

The radical-molecule reaction mechanism of CH3 with NOx (x = 1, 2) has been explored theoretically at the B3LYP/6-311Gd,p and MC-QCISD (single-point) levels of theory. For the singlet potential energy surface (PES) of the CH3 + NO2 reaction, it is found that the carbon to middle nitrogen attack between CH3 and NO2 can form energy-rich adduct a (H3CNO2) with no barrier followed by isomerization to b1 (CH3ONO-trans), which can easily convert to b2 (CH3ONO-cis). Subsequently, starting from b (b1, b2), the most feasible pathway is the direct N-O bond cleavage of b (b1, b2) leading to P1 (CH3O + NO) or the 1,3-H-shift and N-O bond rupture of b1 to form P2 (CH2O + HNO), both of which may have comparable contribution to the reaction CH3 + NO2. Much less competitively, b2 can take a concerted H-shift and N-O bond cleavage to form product P3 (CH2O + HON). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CH3 + NO2 reaction is expected to be rapid, as is consistent with the experimental measurement in quality. For the singlet PES of the CH3 + NO reaction, the major product is found to be P1 (HCN + H2O), whereas the minor products are P2 (HNCO + H2) and P3 (HNC +H2O). The CH3 + NO reaction is predicted to be only of significance at high temperatures because the transition states involved in the most feasible pathways lie almost above the reactants. Compared with the singlet pathways, the triplet pathways may have less contributions to both reactions. The present study may be helpful for further experimental investigation of the title reactions.     

New mechanistic insights to the O(3P) + propene reaction from multiplexed photoionization mass spectrometry

The reaction of O((3)P) with propene (C(3)H(6)) has been examined using tunable vacuum ultraviolet radiation and time-resolved multiplexed photoionization mass spectrometry at 4 Torr and 298 K. The temporal and isomeric resolution of these experiments allow the separation of primary from secondary reaction products and determination of branching ratios of 1.00, 0.91 ± 0.30, and 0.05 ± 0.04 for the primary product channels CH(3) + CH(2)CHO, C(2)H(5) + HCO, and H(2) + CH(3)CHCO, respectively. The H + CH(3)CHCHO product channel was not observable for technical reasons in these experiments, so literature values for the branching fraction of this channel were used to convert the measured product branching ratios to branching fractions. The results of the present study, in combination with past experimental and theoretical studies of O((3)P) + C(3)H(6), identify important pathways leading to products on the C(3)H(6)O potential energy surface (PES). The present results suggest that up to 40% of the total product yield may require intersystem crossing from the initial triplet C(3)H(6)O PES to the lower-lying singlet PES.     

Water-catalyzed gas-phase hydrogen abstraction reactions of CH3O2 and HO2 with HO2: a computational investigation

The gas-phase hydrogen abstraction reactions of CH(3)O(2) and HO(2) with HO(2) in the presence and absence of a single water molecule have been studied at the CCSD(T)/6-311++G(3d,2p)//B3LYP/6-311G(2d,2p) level of theory. The calculated results show that the process for O(3) formation is much faster than that for (1)O(2) and (3)O(2) formation in the water-catalyzed CH(3)O(2) + HO(2) reaction. This is different from the results for the non-catalytic reaction of CH(3)O(2) + HO(2), in which almost only the process for (3)O(2) formation takes place. Unlike CH(3)O(2) + HO(2) reaction in which the preferred process is different in the catalytic and non-catalytic conditions, the channel for (3)O(2) formation is the dominant in both catalytic and non-catalytic HO(2) + HO(2) reactions. Furthermore, the calculated total CVT/SCT rate constants for water-catalyzed and non-catalytic title reactions show that the water molecule doesn't contribute to the rate of CH(3)O(2) + HO(2) reaction though the channel for O(3) formation in this water-catalyzed reaction is more kinetically favorable than its non-catalytic process. Meanwhile, the water molecule plays an important positive role in increasing the rate of HO(2) + HO(2) reaction. These results are in good agreement with available experiments.     

He I photoelectron spectroscopy and theoretical investigation on diaceto disulfide, CH3C(O)OSSOC(O)CH3

A novel species, diaceto disulfide (CH3C(O)OSSOC(O)CH3), has been generated through the heterogeneous reaction between sulfur monochloride (S2Cl2) and silver acetate (AgOC(O)CH3). Photoelectron spectroscopy (PES) and theoretical calculations are performed to investigate its electronic and geometric structures. This molecule exhibits gauche conformation with both C=O groups syn to the S-O bond. The dihedral angle around the S-S bond is calculated to be -93.1 degrees at the B3LYP/6-311++G(3df,3pd) level. After structural optimizations of the most stable conformer, a theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) was performed. The ionization energies of different bands in the photoelectron spectrum are in good agreement with the calculated values from the OVGF method. The first vertical ionization energy of CH3C(O)OSSOC(O)CH3 is determined to be 9.83 eV by photoelectron spectroscopy, which corresponds to the ionization of an electron mainly localized on the sulfur 3p lone pair molecular orbital.     

Selective surface decoration of corannulene

The reaction of corannulene (C(20)H(10)) with 1,2-C(2)H(4)Hal(2) (Hal = Cl or Br) in the presence of AlCl(3) affords stable nonplanar carbocations C(20)H(10)CH(2)CH(2)Hal(+) (Hal = Cl (1) and Br (2)) with an -CH(2)CH(2)Hal moiety attached to the interior carbon atom of the bowl. In the analogous reaction with 1-bromo-2-chloroethane, the selective (up to 98%) abstraction of chloride is observed with the formation of cation 2. The molecular structures of bowl-shaped carbocations 1 and 2 crystallized as salts with AlCl(4)(-) counterions are revealed by single-crystal X-ray diffraction. The reaction of 2 with methanol or ethanol provides further decoration of the nonplanar polyarene upon the nucleophilic addition of alkoxy groups to the exterior carbon atom of the corannulene moiety. The (1)H NMR investigation of the corresponding products, C(20)H(10)(CH(2)CH(2)Br)(OCH(2)R) (R = H (3) and CH(3) (4)), shows the formation of intramolecular H···O and H···Br hydrogen bonds.     

Non-RRKM dynamics in the CH3O2 + NO reaction system

Quasi-classical trajectory (QCT) calculations on a model potential energy surface (PES) show strong deviations from statistical Rice-Ramsperger-Kassel-Marcus (RRKM) rate theory for the decomposition reaction (1) CH3OONO* --> CH3O + NO2, where the highly excited CH3OONO* was formed by (2) CH3O2 + NO --> CH3OONO*. The model PES accurately describes the vibrational frequencies, structures, and thermochemistry of the cis- and trans-CH3OONO isomers; it includes cis-trans isomerization in addition to reactions 1 and 2 but does not include nitrate formation, which is too slow to affect the decay rate of CH3OONO*. The QCT results give a strongly time-dependent rate constant for decomposition and damped oscillations in the decomposition rate, not predicted by statistical rate theory. Anharmonicity is shown to play an important role in reducing the rate constant by a factor of 10 smaller than predicted using classical harmonic RRKM theory (microcanonical variational transition state theory). Master equation simulations of organic nitrate yields published previously by two groups assumed that RRKM theory is accurate for reactions 1 and 2 but required surprising parametrizations to fit experimental nitrate yield data. In the present work, it is hypothesized that the non-RRKM rate of reaction (1) and vibrational anharmonicity are at least partly responsible for the surprising parameters.     

A systematic computational study of the reactions of HO2 with RO2: the HO2 + CH2ClO2, CHCl2O2, and CCl3O2 reactions

Potential energy surfaces for the reactions of HO(2) with CH(2)ClO(2), CHCl(2)O(2), and CCl(3)O(2) have been calculated using coupled cluster theory and density functional theory (B3LYP). It is revealed that all the reactions take place on both singlet and triplet surfaces. Potential wells exist in the entrance channels for both surfaces. The reaction mechanism on the triplet surface is simple, including hydrogen abstraction and S(N)2-type displacement. The reaction mechanism on the singlet surface is more complicated. Interestingly, the corresponding transition states prefer to be 4-, 5-, or 7-member-ring structures. For the HO(2) + CH(2)ClO(2) reaction, there are two major product channels, viz., the formation of CH(2)ClOOH + O(2) via hydrogen abstraction on the triplet surface and the formation of CHClO + OH + HO(2) via a 5-member-ring transition state. Meanwhile, two O(3)-forming channels, namely, CH(2)O + HCl + O(3) and CH(2)ClOH + O(3) might be competitive at elevated temperatures. The HO(2) + CHCl(2)O(2) reaction has a mechanism similar to that of the HO(2) + CH(2)ClO(2) reaction. For the HO(2) + CCl(3)O(2) reaction, the formation of CCl(3)O(2)H + O(2) is the dominant channel. The Cl-substitution effect on the geometries, barriers, and heats of reaction is discussed. In addition, the unimolecular decomposition of the excited ROOH (e.g., CH(2)ClOOH, CHCl(2)OOH, and CCl(3)OOH) molecules has been investigated. The implication of the present mechanisms in atmospheric chemistry is discussed in comparison with the experimental measurements.     

Quantum Chemical Study on the Reaction Mechanism of OBrO Radical with OH Radical

The reaction mechanism of OBrO with OH has been studied using the B3LYP/6-311 G(d,p) and the high-level electron-correlation CCSD(T)/6-311 G(d,p) at single-point. The results show that the title reaction could probably proceed by four possible schemes, generating HOBr O2, HBr O3, BrO HO2 and HOBrO2 products, respectively. The main channel is the one to yield HOBr O2. The whole reaction involves the formation of three-membered, four-membered and five-membered rings, followed by the complicated processes of association,H-shift, Br-shift and dissociation. All routes are exothermic.     

Water-assisted interconversions and dissociations of the acetaldehyde ion and its isomers. An experimental and theoretical study

The gas-phase reactions of the ion [CH(3)CHO/H(2)O](+*) have been investigated by mass spectrometry. The metastable ion (MI) mass spectrum reveals that this ion-molecule complex decomposes spontaneously by the losses of H(2)O, CO, and (*)CH(3). The structures of stable complexes and transition states involved in the potential energy surface (PES) have been studied by the G3//B3-LYP/6-31+G(d) computational method. Hydrogen-bridged water complexes have been found to be the major products of the losses of CO and (*)CH(3). The CO loss produces the [(*)CH(3)...H(3)O(+)] ion and involves a "backside displacement" mechanism. The products corresponding to (*)CH(3) loss have been assigned by theory to be [OC...H(3)O(+)] and [CO...H(3)O(+)], and their 298 K enthalpy values, calculated at the G3 level of theory, are Delta(f)H[OC...H(3)O(+)] = 420 kJ/mol and Delta(f)H[CO...H(3)O(+)] = 448 kJ/mol. The PES describing the interconversions among water-solvated CH(3)CHO(+*), CH(3)COH(+*), and CH(2)CHOH(+*) have been shown to involve proton-transport catalysis (PTC), catalyzed 1,2 H-transfer, and an uncatalyzed H-atom transfer mechanism, respectively.     

Low-energy paths for the unimolecular decomposition of CH3OH: a G2M/statistical theory study

The potential energy surface (PES) of the CH3OH system has been characterized by ab initio molecular orbital theory calculations at the G2M level of theory. The mechanisms for the decomposition of CH3OH and the related bimolecular reactions, CH3 + OH and 1CH2 + H2O, have been elucidated. The rate constants for these processes have been calculated using variational RRKM theory and compared with available experimental data. The total decomposition rate constants of CH3OH at the high- and low-pressure limits can be represented by k infinity = 1.56 x 10(16) exp(-44,310/T) s-1 and kAr0 = 1.60 x 10(36) T-12.2 exp(-48,140/T) cm3 molecule-1 s-1, respectively, covering the temperature range 1000-3000 K, in reasonable agreement with the experimental values. Our results indicate that the product branching ratios are strongly pressure dependent, with the production of CH3 + OH and 1CH2 + H2O dominant under high (P > 10(3) Torr) and low (P < 1 atm) pressures, respectively. For the bimolecular reaction of CH3 and OH, the total rate constant and the yields of 1CH2 + H2O and H2 + HCOH at lower pressures (P < 5 Torr) could be reasonably accounted for by the theory. For the reaction of 1CH2 with H2O, both the yield of CH3 + OH and the total rate constant could also be satisfactorily predicted theoretically. The production of 3CH2 + H2O by the singlet to triplet surface crossing, predicted to occur at 4.3 kcal mol-1 above the H2C...OH2 van der Waals complex (which lies 82.7 kcal mol-1 above CH3OH), was neglected in our calculations.     

Theoretical studies on the thermochemistry of stable closed-shell C1 and C2 brominated hydrocarbons

The enthalpies of formation of stable closed shell C1 and C2 brominated hydrocarbons have been predicted using Gaussian-3X model chemistry. The entropy, heat capacity, and thermal corrections are calculated from B3LYP/6-31G(2df,p) geometries and vibrational frequencies using rigid-rotor-harmonic-oscillator approximation, except for the quantities of the internal rotations in ethanes, which are calculated using the quantum-mechanical energy levels. Enthalpies of formation have been obtained from G3X atomization and isodesmic reactions. Good agreement is observed on the well-established experimental enthalpies of formation of CH 3Br, CH 2Br 2, CH 2ClBr, and C 2H 3Br from the high-resolution threshold photoelectron photoionization coincidence study.     

Thermal stability of carbonyl radicals. Part II. Reactions of methylglyoxyl and methylglyoxylperoxy radicals at 1 bar in the temperature range 275-311 K

Reactions of methylglyoxyl and methylglyoxylperoxy radicals were investigated at a total pressure of 1 bar in oxygen. Methylglyoxyl radicals were generated by stationary photolysis of Br2-CH3C(O)C(O)H-NO2-O2-N2 mixtures at wavelengths > or =480 nm and of Cl2-CH3C(O)C(O)H-NO2-O2-N2 mixtures in the wavelength range 315-460 nm. In the bromine system, rate constant ratios for the reactions CH3C(O)CO --> CH3CO + CO (kdis) and CH3C(O)CO + O2 --> CH3C(O)C(O)O2 (kO2) were measured as a function of temperature in the range 275-311 K. Assuming the constant value kO2 = 5.1 x 10(-12) cm3 molecule(-1) s(-1) for our reaction conditions, kdis = 1.2 x 10(10.0+/-0.7) x exp(-11.7 +/- 3.8 kJ mol(-1)/RT) s(-1) (2sigma errors) was obtained for ptot = 1 bar (M = O2), in good agreement with the kinetic parameters calculated by Méreau et al. [R. Méreau, M.-T. Rayez, J.-C. Rayez, F. Caralp and R. Lesclaux, Phys. Chem. Chem. Phys., 2001, 3, 4712]. CH3C(O)C(O)O2 radicals oxidise NO2, forming NO3, CH3CO and CO2. This experimental result is supported by DFT and ab initio calculations. Possible mechanisms for the observed formation of several % of ketene and bromoacetyl peroxynitrate are discussed. Use of Cl rather than Br atoms to abstract the aldehydic H atom from methylglyoxal leads to chemically activated CH3C(O)CO radicals, thus substantially increasing the fraction of CH3C(O)CO radicals that decompose rather than add O2.     

Selenoether macrocyclic chemistry--syntheses and properties of new potentially tridentate and hexadentate Se/O-donor macrocycles

Treatment of O(CH2CH2SeCN)2 with Na in NH3(l), followed by dropwise addition of a thf solution of o-C6H4(CH2Br)2 at -40 degrees C leads to formation of three mixed Se/O-donor macrocycles which are separable by column chromatography, the [1 + 1] species L1, the [2 + 2] ring L2 and the [3 + 3] ring L3, of which L2 is by far the major species. Using the same starting materials, but in a high dilution cyclisation at room temperature with NaBH4 in thf/EtOH gives exclusively the [1 + 1] ring, L1. The saturated ring Se/O-donor macrocycles, L4 and L5 are obtained by simultaneous dropwise addition of solutions of O(CH2CH2SeCN)2 and Br(CH2)3Br to NaBH4 suspended in thf/EtOH. The small tridentate Se2O-donor ring, L4, is again the dominant product under these conditions (71%), although the more flexible precursors in this reaction also give rise to the larger Se4O2-donor ring, L5, as a by-product in 8% yield. These compounds are readily separated and purified by column chromatography (ethyl acetate:hexane, 1:19). The new macrocycles have been characterised by 1H, (13)C{1H} and (77)Se{1H} NMR spectroscopy and mass spectrometry, together with crystal structures of L1 and L2. Complexes of L1 and L2 with late transition metals (Pd(II), Pt(II), Cu(I) and Ag(I)) are also described.