Reaction of CH3CHO with Y+: A density functional theoretical study

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.     

Gas-phase reactions of pd with acetone: A theoretical investigation using density functional theory

The gas-phase reaction of palladium atom with acetone is investigated using density functional theory. Geometries and energies of the reactants, intermediates, and products involved are calculated. 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 an ??²-CH₃COCH₃-metal complex, followed by C-O, C-H, and C-C activation. These reactions can lead to four different products (PdO + C₃H₆, PdCH₂COCH₃ + H, PdCH₂ + CH₃CHO, and PdCOCH₂ + CH₄). The present results may be helpful in understanding the mechanism of the title reaction and further experimental investigation of the reaction.     

Reaction of propionitrile with methylidyne: A theoretical study

The results of a CCSD(T)-F12/cc-pVTZ-f12//ωB97XD/cc-pVTZ quantum-chemical study of the potential energy surface (PES) for the reaction of propionitrile with methylidyne are combined with Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the reaction rate constants and product branching ratios in the deep space conditions corresponding to the zero-pressure limit at various collision energies. The most energetically favorable reaction pathways have been identified. The reaction outcome has been shown to strongly depend on the branching in the entrance reaction channel, between CH additions and insertions into various C-H and C-C bonds. For instance, CH addition to the N atom predominantly leads to 3H-pyrrole + H (p9), with CH₂NC + C₂H₄ (p2) also being a significant product. CH addition to the triple C≡N bond mostly results in 2-methylene-2H-azirine + CH₃ (p13), whereas CH insertions into C-H bonds in the CH₃ and CH₂ groups of propionitrile form CH₂CN + C₂H₄ (p1) and CH₂CHCN + CH₃ (p7) respectively. Less likely CH insertions into single C-C bonds yield CH₃CHCHCN + H (p5) and CH₂CHCH₂CN + H (p8). The results indicate that the methylidyne + propionitrile reaction may represent a critical step toward the formation of heterocyclic N-containing molecules in the interstellar medium and in planetary atmospheres.     

DFT investigation of the mechanism of CH2CO + O(3P) reaction

A detailed theoretical survey of the potential energy surface (PES) for the CH₂CO + O(³P) reaction is carried out at the QCISD(T)/6‐311+G(3df,2p)//B3LYP/6‐311+G(d,p) level. The geometries, vibrational frequencies, and energies of all stationary points involved in the reaction are calculated at the B3LYP/6‐311+G(d,p) level. More accurate energy information is provided by single‐point calculations at the QCISD(T)/6‐311+G(3df,2p) level. Relationships of the reactants, transition states, intermediates, and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. The results suggest that P1(CH₂+CO₂) is the most important product. This study presents highlights of the mechanism of the title reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Imaging the Reaction Dynamics of O(3P)+CH4→OH+CH3

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.     

Theoretical study of the mechanism of CH2CO + CN reaction

The potential energy surface information of the CH₂CO + CN reaction is obtained at the B3LYP/6‐311+G(d,p) level. To gain further mechanistic knowledge, higher‐level single‐point calculations for the stationary points are performed at the QCISD(T)/6‐311++G(d,p) level. The CH₂CO + CN reaction proceeds through four possible mechanisms: direct hydrogen abstraction, olefinic carbon addition–elimination, carbonyl carbon addition–elimination, and side oxygen addition–elimination. Our calculations demonstrate that R→IM1→TS3→P3: CH₂CN + CO is the energetically favorable channel; however, channel R→IM2→TS4→P4: CH₂NC + CO is considerably competitive, especially as the temperature increases (R, IM, TS, and P represent reactant, intermediate, transition state, and product, respectively). The present study may be helpful in probing the mechanism of the CH₂CO + CN reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Transition state theory thermal rate constants and RRKM‐based branching ratios for the N(2D) + CH4 reaction based on multi‐sState and multi‐reference Ab Initio calculations of interest for the titan's chemistry

Multireference single and double configuration interaction (MRCI) calculations including Davidson (+Q) or Pople (+P) corrections have been conducted in this work for the reactants, products, and extrema of the doublet ground state potential energy surface involved in the N( ² D) + CH₄ reaction. Such highly correlated ab initio calculations are then compared with previous PMP4, CCSD(T), W1, and DFT/B3LYP studies. Large relative differences are observed in particular for the transition state in the entrance channel resolving the disagreement between previous ab initio calculations. We confirm the existence of a small but positive potential barrier (3.86 ± 0.84 kJ mol^?1 (MR‐AQCC) and 3.89 kJ mol^?1 (MRCI+P)) in the entrance channel of the title reaction. The correlation is seen to change significantly the energetic position of the two minima and five saddle points of this system together with the dissociation channels but not their relative order. The influence of the electronic correlation into the energetic of the system is clearly demonstrated by the thermal rate constant evaluation and it temperature dependance by means of the transition state theory. Indeed, only MRCI values are able to reproduce the experimental rate constant of the title reaction and its behavior with temperature. Similarly, product branching ratios, evaluated by means of unimolecular RRKM theory, confirm the NH production of Umemoto et al., whereas previous works based on less accurate ab initio calculations failed. We confirm the previous findings that the N( ² D) + CH₄ reaction proceeds via an insertion–dissociation mechanism and that the dominant product channels are CH₂NH + H and CH₃ + NH. © 2012 Wiley Periodicals, Inc.     

DFT studies on the multi‐channel reaction of CH3S+NO2

The mechanisms for the reaction of CH₃S with NO₂ are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) on both single and triple potential energy surfaces (PESs). The geometries, vibrational frequencies, and zero‐point energy (ZPE) correction of all stationary points involved in the title reaction are calculated at the B3LYP/6‐311++G(d,p) level. More accurate energies are obtained at the QCISD(T)/6‐311++G(d,p). The results show that 5 intermediates and 14 transition states are found. The reaction is more predominant on the single PES, while it is negligible on the triple PES. Without any barrier height for the whole process, the main channel of the reaction is to form CH₃SONO and then dissociate to CH₃SO+NO. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

A density functional theory study on the atmospheric reaction of CH3O2 with HS: Mechanism and kinetics

The reaction mechanism of CH₃O₂ and HS was systematically investigated by density functional theory (DFT). Six singlet pathways and seven triplet ones are located on the potential surface (PES). The result indicates that the main products are CH₃O and HSO both on the singlet and triplet PES, different from the CH₃O₂ + OH reaction. Moreover, deformation density (ρ_def) and atoms in molecules (AIM) analyses were carried out to further uncover the nature of chemical bonding evolution in the primary pathways. Furthermore, reaction rate constants were calculated in the temperature range from 200 to 1000 K using the transition state theory with the Wigner and Eckart tunneling corrections. Our results can shed light on the title reaction and offer instructions for analogous atmospheric reactions, as well as experimental research in the future.     

On the kinetic mechanism of reactions of hydroxyl radical with CHF2CH3 − n F n (n = 1–3)

The potential energy surfaces of the reactions CHF₂CH_3 − n F _n (n = 1–3) + OH were investigated by MPWB1K and BMC-CCSD (single-point) methods. Furthermore, with the aid of canonical variational transition state theory including the small-curvature tunneling correction, the rate constants of the title reactions were calculated over a wide temperature range of 220–1,500 K. Agreement between the CVT/SCT rate constants and the experimental values is good. Our results show that the order of rate constants is CHF₂CH₂F + OH > CHF₂CHF₂ + OH > CHF₂CF₃ + OH. For reaction CHF₂CH₂F + OH, the 1-H-abstraction channel dominates the reaction at the whole temperature, while 2-H-abstraction channel appears to be competitive with the increase of temperature.     

Computational study on the mechanism for the gas‐phase reaction of dimethyl disulfide with OH

The mechanisms for the reaction of CH₃SSCH₃ with OH radical are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) level of theory. Five channels have been obtained and six transition state structures have been located for the title reaction. The initial association between CH₃SSCH₃ and OH, which forms two low‐energy adducts named as CH₃S(OH)SCH₃ (IM1 and IM2), is confirmed to be a barrierless process, The S? S bond rupture and H? S bond formation of IM1 lead to the products P1(CH₃SH + CH₃SO) with a barrier height of 40.00 kJ mol^?1. The reaction energy of Path 1 is ?74.04 kJ mol^?1. P1 is the most abundant in view of both thermodynamics and dynamics. In addition, IMs can lead to the products P2 (CH₃S + CH₃SOH), P3 (H₂O + CH₂S + CH₃S), P4 (CH₃ + CH₃SSOH), and P5 (CH₄ + CH₃SSO) by addition‐elimination or hydrogen abstraction mechanism. All products are thermodynamically favorable except for P4 (CH₃ + CH₃SSOH). The reaction energies of Path 2, Path 3, Path 4, and Path 5 are ?28.42, ?46.90, 28.03, and ?89.47 kJ mol^?1, respectively. Path 5 is the least favorable channel despite its largest exothermicity (?89.47 kJ mol^?1) because this process must undergo two barriers of TS5 (109.0 kJ mol^?1) and TS6 (25.49 kJ mol^?1). Hopefully, the results presented in this study may provide helpful information on deep insight into the reaction mechanism. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study on the atmospheric reaction of CH3O2 with OH

A quantum chemical investigation on the reaction mechanism of CH₃O₂ with OH has been performed. Based on B3LYP and QCISD(T) calculations, seven possible singlet pathways and seven possible triplet pathways have been found. On the singlet potential energy surface (PES), the most favorable channel starts with a barrierless addition of O atom to CH₃O₂ leading to CH₃OOOH and then the O? O bond dissociates to give out CH₃O + HO₂. On the triplet PES, the calculations indicate that the dominant products should be ³CH₂O₂ + H₂O with an energy barrier of 29.95 kJ/mol. The results obtained in this work enrich the theoretical information of the title reaction and provide guidance for analogous atmospheric chemistry reactions. © 2015 Wiley Periodicals, Inc.     

Quantum chemical study on insertion and abstraction reaction of dichlorocarbene with methyl alcohol and methyl mercaptan

The insertion and abstraction reaction mechanisms of singlet and triplet CCl₂ with CH₃MH (M=O, S) have been studied by using the DFT, NBO and AIM methods. The geometries of reactions, the transition state and products were completely optimized by B3LYP/6–311G(d, p). All the energy of the species was obtained at the CCSD(T)/6–311G(d, p) level. The calculated results indicated that the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CCl₂ can not only trigger the insertion reaction with C-H and M-H in four pathways, by which the products P1 [CH₃OCHCl₂, reaction I(1)], P3[Cl₂HCCH₂OH, reaction I(2)], P5[CH₃SCHCl₂, reaction II(1)] and P7[Cl₂HCCH₂SH, reaction II(2)] are produced respectively, but also abstract M-H, resulting P4 [CH₂O+CH₂Cl₂, reaction I(3)] and P8[CH₂S+CH₂Cl₂, reaction II(3)]. In addition, the important geometries in domain pathways have been studied by AIM and NBO theories. Supported by the National Natural Science Foundation of China (Grant No. 20335030) and Foundation of Education Committee of Gansu Province (Grant No. 0708-11)     

Ab initio study of the potential energy surface and product branching ratios for the reaction of O(1D) with CH3CH2Br

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     

Theoretical study on the partial potential energy surface and formation mechanism of the reactive resonance state of HO + CH4 → H2O + CH3 system

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     

Theoretical study on the reaction mechanism of CN radical with ketene

The bimolecular single collision reaction potential energy surface of CN radical with ketene (CH2CO) was investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH2CO to form the intermediate NCCH2CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH2CN CO. The second is a direct addition reaction between CN and CH2CO to form the intermediate CH2C(O)CN followed by its isomerization into NCCH2CO via a CN-shift reaction, and subsequently, NCCH2CO dissociates into CH2CN CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH2CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The present theoretical computation results, which give an available suggestion on the reaction mechanism, are in good agreement with previous experimental studies.     

Theoretical study of model elementary reactions of dissociative addition of light hydrocarbons to the Ti-doped aluminide cluster Al<Subscript>12</Subscript>Ti

The potential energy surfaces (PES), energies E, and activation barriers h of elementary reactions of dissociative addition of CH₄ and C₂H₆ molecules to the Al₁₂Ti cluster with a marquee structure in the singlet and triplet states were calculated within the B3LYP approximation of the density functional theory using the 6-31G* basis set. The first stage of the reaction Al₁₂Ti + CH₄ leads to the adsorption complex CH₄ · Al₁₂Ti with the R(TiC) distance of ～2.4 Å. The methane molecule is coordinated as a tridentate ligand the singlet state and as a bidentate ligand in the triplet state, although both coordination modes are close in energy. In the transition state, the CH₄ molecule is coordinated through its active C-H bond to an inclined Ti-Al edge of the cluster, and the C-H bond is significantly elongated and weakened. The activation barrier height h referenced to the CH₄ complex is ～9 and ～19 kcal/mol for the singlet and triplet, respectively, and that referenced to the primary products Al₁₂Ti(CH₃)(H) is ～21 kcal/mol. The barrier to migration of the CH₃ group around the metal cluster is estimated at ～10 kcal/mol. At the initial stage of the reaction Al₁₂Ti + C₂H₆, two types of C₂H₆ · Al₁₂Ti adsorption complexes are formed. In one of them, the ethane molecule is coordinated through a methyl group (as the methane molecule); and in the other type, the coordination is through the C-C bond. This reaction can proceed through two paths by means of insertion into C-H or C-C bonds to give Al₁₂Ti(C₂H₅)(H) or Al₁₂Ti(CH₃)₂, respectively. The second path is impeded by a high barrier (～30 kcal/mol) and is possible, if at all, only at high temperatures. Conversely, the insertion into a C-H bond in ethane is somewhat more favorable than in methane. Analogously, the PES of addition of the second methane molecule to Al₁₂Ti(CH₃)(H) was calculated. The second molecule is adsorbed and dissociates by the same mechanism as the first CH₄ molecule, but with somewhat lower barriers and energy effect of formation of Al₁₂Ti(CH₃)₂(H)₂. The addition of propane and longer hydrocarbons is briefly considered. The results are compared with the results of previous analogous calculations of the PES of related reactions of dissociative adsorption of dihydrogen on the Al₁₂Ti cluster, which are more exothermic, have lower barriers, and can occur under milder conditions.     

The DFT study on mechanisms for NCO with C2H5 reaction

A detailed investigation has been performed at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311+G(d,p) level for the reaction of NCO with C₂H₅ by constructing singlet and triplet potential energy surfaces (PES). The results show that the title reaction is more favorable on the singlet PES than on the triplet PES. On the singlet PES, the initial addition processes are barrierless and release lots of energy. The dominant channel occurs via the fragmentations of the initial adduct C₂H₅NCO and C₂H₅OCN to form C₂H₄ + HNCO and HOCN, respectively. With higher barrier heights, other products such as CH₄ + HNC + CO, CH₃CHNH + CO, CH₃CH + HNCO, and CH₃CN + H₂ + CO are less competitive. On the triplet PES, the entrance reactions surpass significant barriers; therefore, it could be negligible at the normal atmospheric condition. However, the most feasible channel on the triplet PES is the direct hydrogen abstraction channel to form CH₂CH₂ + HNCO. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Ab initio and RRKM calculations for the reaction channels of O(1D) + CH3CHF2

Ab initio and Rice–Ramsperger–Kassel–Marcus theories are carried out to study the potential energy surface and the energy‐dependent rate constants and branching ratios of the products for O(¹D) + CH₃CHF₂ reaction. Optimized geometries and vibrational frequencies have been obtained by MP2/6‐311G(d,p) method. The main products of the title reaction are CH₃CFO + HF, CH₂CFOH + HF, and CH₃ + CF₂OH at lower collision energy; and CH₃ + CF₂OH, CH₃CF₂ + OH are the main products at higher collision energy. CHF₂ + CH₂OH are the main products in the whole range of collision energy. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Co3O4纳米晶催化氧化甲烷的理论研究：C-H键活化的晶面效应及活性中心

甲烷是一种在自然界中大量存在的原材料,在取代原油和合成重要化工产品等许多领域具有潜在的应用价值. 然而,由于CH₄中C-H键的键能特别大（约~4.5 eV）,如何实现甲烷的绿色有效转化在化学化工领域仍然是一个挑战. 本文采用密度泛函理论对Co₃O₄（001）和（011）晶面活化甲烷C-H键的机理进行了理论研究,得到了如下结论：（1） CH₄的C-H键在Co₃O₄晶面的解离具有很高的活性,只需要克服大约1 eV的能垒;（2）与Co^2＋相连的Co-O离子对是CH₄活化的活性位点,其中两个带正负电荷的离子对C-H解离起着协同作用,帮助产生Co-CH₃和O-H物种;（3）（011）面的反应活性明显大于（001）面,与实验的观察一致. 本文的计算结果表明,Co₃O₄纳米晶面对CH₄中C-H键的活化表现出明显的晶面效应和结构敏感效应,Co-O离子对活性中心对于活化惰性的C-H键发挥了关键作用.