Profile Of Potential Energy Surface Research Articles

Atomic-level understanding on conformational flexibility of neochlorogenic and chlorogenic acids and their inclusion complexation with β-cyclodextrin

Neochlorogenic acid (NCA) and chlorogenic acid (CGA) are positional isomers, abundant in plums and prunes. Their limited bioavailability due to instability under ambient conditions can be overcome by cyclodexrin (CD) encapsulation. Here, single-crystal X-ray diffraction combined with density functional theory (DFT) calculation has been carried out on NCA in free form (1) and in complex with β-CD (2), providing atomic-level insights into the structural flexibility and the inclusion complexation with β-CD of CGA isomers. X-ray analysis revealed that the two symmetry-independent s-cis-NCA and 0.3 water molecules form elaborated H-bond networks (1). Upon β-CD encapsulation, complex H-bond patterns are disrupted and the converted s-trans-NCA is almost entirely enclosed in the asymmetric capsular β-CD dimer (2). On the contrary, the twofold symmetry-related β-CD–s-cis-CGA dimer forms a rare [4]pseudorotaxane reported previously. DFT full-geometry optimization disclosed that both the 2:1 and 1:1 trimodal β-CD–s-trans-NCA inclusion complexes are energetically stable, as the reported s-cis-CGA complex. Furthermore, the three-dimension potential energy surface (3D PES) profiles and all the DFT-fully optimized NCA and CGA structures existing in different lattice environments showed that both the s-cis and s-trans conformers are thermodynamically stable. This study not only presents crystallographic evidence for the distinct NCA and CGA conformers, unequivocally differentiating and resolving the long-time confusing CGA nomenclature for the first time, but also highlights the prime role of CGA conformational flexibility in their pharmacological functions.

Nonadiabatic molecular dynamics simulations for ultrafast photo-induced ring-opening and isomerization reactions of 2,2-diphenyl-2H-chromene.

Nonadiabatic molecular dynamics simulations with a global switching algorithm have been performed at the TD-CAM-B3LYP-D3/def2-SVP level of theory for ultrafast photo-induced ring-opening and isomerization reactions upon S1 excitation for 2,2-diphenyl-2H-chromene (DPC). Both DPC-T and DPC-C conformers undergo ring-opening relaxation and isomerization pathways accompanied with pyran conformation conserved and converted on the S1 or S0 states via competition and cooperation between C-O bond dissociation and pyran inversion motions. Upon S1 excitation, the DPC-T mainly relaxes to the T-type conical intersection region and thus yields a higher ring-opening efficiency with a faster S1 decay and intermediate formation than those of the DPC-C mainly relaxing to C-type conical intersection. The simulated ring-opening quantum yield for DPC-T (DPC-C) is 0.91 (0.76), which is in good agreement with the experimental value of 0.7-0.9, and the thermal weight averaged lifetimes are estimated as 182.0 fs, 228.6 fs, and 1262.4 fs for the excited-state decay, intermediate formation, and ring-opening product, respectively. These time constants are in good agreement with the experimentally measured τ1 time constant of 190-450 fs and τ2 time constant of 1000-1800 fs. The present work could be a valuable reference for understanding the nature of the photorelaxation mechanisms of DPC, and could help to develop DPC-based photoresponsive materials.

A DFT Study on the Binuclear Copper(I)-Catalyzed Synthesis Mechanism of 1,2,3-Triazolo[1,5-c]Pyrimidine via Interrupted Click and Ketenimine Rearrangement.

In this paper, the mechanism of the full catalytic cycle for binuclear Cu(I)-catalyzed sulfonyl azide-alkyne cycloaddition reaction for the synthesis of triazolopyrimidines was rationalized by density functional theoretical (DFT) calculations. The computed reaction route consists of: (a) formation of dicopper intermediates, including C-H activation of terminal alkyne, 3+2 ring cycloaddition and ring-reducing reaction and transmetalation, (b) interrupted CuAAC reaction, including di-copper catalyzed ring-opening of 2H-azirines and C-C bond formation to generate the copper-triazoles and -ketenimines, (c) two-step C-N cross-coupling and following (d) multi-step hydrogen transfer by the hydrogen bonding chain of water to promote the C-N formation and another C-N cleavage through the removal of p-tolyl sulfonamides. Our DFT results indicate that the multi-step hydrogen transfer process is the rate-determining step along the potential energy surface profile. The explicit water model was used for systematic determination of barrier for C-C cross-coupling, C-N bond formation and cleavage, and p-tolylsulfonamide removal. A critical insight in the interrupted CuAAC reaction was proposed. Further prediction interprets H2 O hydrogen bond chain plays an important role in C-N bond formation and cleavage, and the removal of p-tolylsulfonamide. This may have fundamental guidance on the design of 1, 5-herterocyclic functionalized triazolopyrimidines via interrupted CuAAC rearrangement reaction, as well as hydrogen bond chain of water.

Experimental evidences and theoretical calculations on phenanthrene degradation in a solar-light-driven photocatalysis system using silica aerogel supported TiO2 nanoparticles: Insights into reactive sites and energy evolution

Quantitative identification on reactive sites of target organic molecule during photocatalysis can help to get deep insight into the pollutant degradation pathway and energy evolution process. In this study, a new class of silica aerogel supported TiO2 (TiO2/SiO2) photocatalysts were fabricated via a two-step approach, and applied for adsorption and photocatalytic degradation of phenanthrene. Anatase crystalline structure was formed upon calcination at 400 and 600 °C, while mixed crystal interphases of anatase and rutile were generated at 800 °C (anatase:rutile = 0.67:0.33). The higher calcination temperature resulted in better crystallinity of TiO2, higher photocatalytic activity, and reduced adsorption affinity toward phenanthrene. TiO2/SiO2-800 (TiO2/SiO2 calcined at 800 °C) showed minimal phenanthrene uptake (~5.2%) but the strongest photocatalytic activity, and it was able to completely degrade phenanthrene within 3 h. The SiO2 aerogel component in the composite enabled the pre-concentration of phenanthrene on the photoactive sites, while the nanoscale mixed-phases of anatase and rutile of TiO2/SiO2-800 act as an efficient transfer medium for photo-induced charge carriers. Moreover, the formed Ti–O–Si linkage in TiO2/SiO2-800 induced formation of Ti3+ under solar light irradiation, promoting photoexcited electron trap and separation of electron-hole pairs. Based on the degraded phenanthrene intermediates/products, theoretical calculations according to the density functional theory (DFT) reveal that the atoms of phenanthrene with high electrophilic Fukui index (f-) are the most reactive sites towards the radicals. Potential energy surface profile for phenanthrene degradation further reveals the intermediates energy evaluation via radicals attack.

Dynamics and Multiconfiguration Potential Energy Surface for the Singlet O2 Reactions with Radical Cations of Guanine, 9-Methylguanine, 2'-Deoxyguanosine, and Guanosine.

Reactions of electronically excited singlet oxygen (1O2) with the radical cations of guanine (9HG•+), 9-methylguanine (9MG•+), 2'-deoxyguanosine (dGuo•+), and guanosine (Guo•+) were studied in the gas phase by a combination of guided-ion-beam mass spectrometric measurement of product ions and cross sections as a function of collision energy (Ecol) and electronic structure calculations of the reaction potential energy surface (PES) at various levels of theory. No product could be captured in the 1O2 reaction with bare 9HG•+ or 9MG•+, because energized products decayed rapidly to reactants before being detected. To overcome this unfavorable kinetics, monohydrated 9HG•+·H2O and 9MG•+·H2O were used as reactant ions, of which the peroxide product ions were stabilized by energy relaxation via elimination of the water ligand. Reaction cross sections for 9HG•+·H2O and 9MG•+·H2O decrease with increasing Ecol, becoming negligible above 0.6 eV. This indicates that the reactions are exothermic with no barriers above reactants and the heat of formation of the products is sufficiently large to overcome their water ligand elimination energy (0.7 eV). Peroxide product ions were also detected in the 1O2 reactions with unhydrated dGuo•+ and Guo•+, in which intramolecular vibrational redistribution was able to stabilize oxidation products. 9MG•+ was utilized as a model system to explore the reaction PES for the initial 1O2 addition to the guanine radical cation. Calculations were carried out using single-reference ωB97XD, RI-MP2, and DLPNO-CCSD(T) and multireference CASSCF and CASPT2. Although the same PES profile was obtained at different levels of theory, the energies of the mixed open- and closed-shell 1O2 reactant and the open-shell reaction intermediates, transition states, and products are sensitive to the theories. By taking into account both static and dynamic electron correlations, the CASPT2 PES has provided the best agreement with the experimentally measured reaction thermodynamics and predicted 8-peroxide as the most probable initial oxidation product of the guanine radical cation.

Photoisomerization-mechanism-associated excited-state hydrogen transfer in 2'-hydroxychalcone revealed by on-the-fly trajectory surface-hopping molecular dynamics simulation.

By performing global-switching on-the-fly trajectory surface-hopping molecular dynamics simulation at the OM2/MRCI (14,15) quantum level, we probed the S3(ππ*) photoisomerization mechanisms associated with excited-state intramolecular hydrogen transfer for 2'-hydroxychalcone (2HC) within the interwoven conical intersection networks from four singlet electronic states (S3, S2, S1, and S0). The simulated quantum yields of 0.03 for cis-to-trans and zero for trans-to-cis photoisomerization were due to almost all the conical intersections being localized either in the cis-2HC or in trans-2HC region, and there was little chance for sampling trajectories to reach the rotation conical intersection (S1/S0) in between cis-2HC and trans-2HC that is key for reactive isomerization. The potential energy well on the S1 state in the trans-2HC region prevents trajectories from trans-to-cis photoisomerization, while the fact there is no well on S1 state in cis-2HC region opens a few chances for trajectories to reach the rotation conical intersections. The present simulation found that excited-state intramolecular hydrogen transfers in 2HC have a negative impact for reactive isomerization, and that hydrogen transfers take place on the S1 state, while back-transfer on the S0 state prevents sampling trajectories reaching rotational conical intersections. It was realized that it could be possible to enhance the quantum yield of 2HC photoisomerization by suppressing the hydrogen transfer (such as by changing an electron-donating substitution or adjusting the substitution position to decrease the acidity of the phenol group). From a perspective view of the potential energy surfaces, the theoretical design of such 2HC derivatives could enhance (control) the quantum yield by shifting the conical intersections away from the cis- and trans-region.

Adsorption of Acetone and Toluene on Single-Vacancy Silicene by Density Functional Theory Calculations

In this work, we investigated the adsorption mechanism of acetone and toluene on the surface of single-vacancy silicene by Density Functional Theory method with taking into account the van der Waals interaction via the optPBE-vdW functional. The potential energy surface and adsorption energy profile are obtained by using the Computational DFT–based Nanoscope tool. It is found that acetone prefers an inclined configuration while toluene favors the parallel one towards the substrate. The single-vacancy silicene maintains its metallic electronic structure after adsorption. The adsorption energies for acetone and toluene adsorptions are −0.36 eV and −0.57 eV, respectively. The Bader charge analysis shows a charge transfer of 0.17e and 0.30e for adsorption of acetone and toluene on silicene, respectively.

A deeper computational look at Mumm rearrangement: Evaluation of substituent, solvent, and temperature effects

AbstractThe effect of substitution, solvent, and temperature on Mumm rearrangement has been investigated using density functional theory (DFT). A potential energy surface (PES) profiles of transition state (TS) is demonstrated to illustrate the alteration of ΔG‡ of Mumm rearrangements for various substitutions. The possible reasons have been studied for the impressive conditions needed for Mumm rearrangement.

Mechanistic Insights into Selective CO2 Conversion via RWGS on Transition Metal Phosphides: A DFT Study

Selective conversion of CO2 to CO via the reverse water gas shift (RWGS) reaction is an attractive CO2 conversion process, which may be integrated with many industrial catalytic processes such as Fischer−Tropsch synthesis to generate added value products. The development of active and cost friendly catalysts is of paramount importance. Among the available catalyst materials, transition metal phosphides (TMPs) such as MoP and Ni2P have remained unexplored in the context of the RWGS reaction. In the present work, we have employed density functional theory (DFT) to first investigate the stability and geometries of selected RWGS intermediates on the MoP (0001) surface, in comparison to the Ni2P (0001) surface. Higher adsorption energies and Bader charges are observed on MoP (0001), indicating better stability of intermediates on the MoP (0001) surface. Furthermore, mechanistic investigation using potential energy surface (PES) profiles showcased that both MoP and Ni2P were active toward RWGS reaction with the direct path (CO2* → CO* + O*) favorable on MoP (0001), whereas the COOH-mediated path (CO2* + H* → COOH*) favors Ni2P (0001) for product (CO and H2O) gas generation. Additionally, PES profiles of initial steps to CO activation revealed that direct CO decomposition to C* and O* is favored only on MoP (0001), while H-assisted CO activation is more favorable on Ni2P (0001) but could also occur on MoP (0001). Furthermore, our DFT calculations also ascertained the possibility of methane formation on Ni2P (0001) during the RWGS process, while MoP (0001) remained more selective toward CO generation.

Methane pyrolysis in preparation of pyrolytic carbon: Thermodynamic and kinetic analysis by density functional theory

The density functional theory has been successfully applied in analyzing pyrolytic carbon deposition by methane pyrolysis from the view of thermodynamics and kinetics based on a total number of 39 elementary reactions. M06-2X/def2-TZVP level was employed to optimize species structures and locate the transition states. The enthalpy changes and Gibbs free energy changes of all the reactions in the temperature range of 298.15–1800 K were derived with optimized species. Results show that the reacting temperature should be above 1200 K based on the equilibrium constant analysis, which is consistent with the typical reaction temperature adopted in experiments. Potential energy surface profiles report that radical attacking reactions have lower energy barriers than those direct decomposition reactions, especially hydrogen radical attacking reactions. The energy barriers of the first steps, dehydrogenations of methane and ethylene, are 272.4 kJ·mol−1 and 288.9 kJ·mol−1 at 1200 K, which are very close to the experimental activation energy for methane pyrolysis. The most favorable decomposition reaction path is the path of hydrogen radical attacking reactions. The highest energy barrier of the path at 1200 K is 185.7 kJ·mol−1 presented by the C–H bond breaking in ethynyl attacked by hydrogen radical.

Theoretical study of the reaction mechanism and kinetics of the OH + trimethyl orthoformate ((CH3O)3CH) + O2 reaction

The profiles of potential energy surface (PES) of Trimethyl orthoformate (TMOF) with OH radicals under atmospheric conditions have been studied by performing M06-2X-GD3/6-311++G(d,p) approach for geometry optimization and ab initio method QCISD (T)/6-311++G(d,p) for energy calculations. The reaction of the OH radicals with TMOF in the presence of O2 is found to form mainly OH radicals, 2,2-dimethoxy-1,3-dioxetane, dimethyl carbonate [(CH3O)2CO] and HC(O)H. Regeneration of OH radicals for the TMOF + OH + O2 reaction is verified in the present calculations, which is consistent with the experimental observations. Based on the PES of the TMOF + OH reaction, temperature-dependent rate coefficients and branching ratios at 298–1500 K are determined using the conventional transition state theory. At 298 K, the calculated individual rate coefficients for H-abstraction from the CH site and the CH3O site of TMOF are 3.90 × 10−12 and 1.58 × 10−12 cm3 molecule−1 s−1, respectively. It is found that ∼71% of the TMOF + OH reaction takes place through the CH site H-abstraction and ∼29% of the TMOF + OH reaction belongs to the CH3O site H-abstraction. The overall rate coefficient displays opposite temperature dependencies at low and high temperatures, viz., negative at low temperatures and positive at high temperatures. In the temperature range of 298–1500 K, the calculated overall rate coefficients can be expressed by the three-parameter Arrhenius equation: k (298–1500 K) = 1.02 × 10−13 × (T/298)3.4 × exp(9885/RT) cm3 molecule−1 s−1.

Role of Complexation between Monomethylamine and Triplet Nitromethane Molecules in the Hydrogen Transfer Reaction

The mechanism of photochemical hydrogen atom transfer from an amine to a triplet nitro compound has been studied using monomethylamine and triplet nitromethane as an example. Two variants of the reaction have been considered: the transfer of hydrogen from the amino group and from the methyl group. The simulation has been carried out by quantum chemistry methods using the B2PLYP/cc-pVDZ functional. Complexation in pre- and postreaction complexes has been shown in terms of the theory of atoms in molecules. The profiles of potential energy surface of the reactions have been constructed. It has been concluded that the reaction of hydrogen transfer from the methyl group is energetically more favorable. It has been established that a strong hydrogen-bonded complex is formed during the reaction.

The gas-phase pyrolysis of methyl azidoformate in the absence and presence of water: a theoretical study

ABSTRACTThe potential energy surface profiles for the gas-phase pyrolysis of methyl azidoformate (MA, CH3OC(O)N3) in the absence and presence of one water molecule have been investigated by ab initio methods at CCSD(T)/6-311++G(2df,2pd)//MP2(full)/6-311++G(d,p)+0.95×ZPE levels of theory. Three types of mechanisms are discussed for the gas-phase decomposition of CH3OC(O)N3. Ab initio calculations show that a four-membered-ring intermediate can be formed by the stepwise routes. The resulting intermediate can undergo two competitive decomposition channels to generate the major products CO2 + CH2 = NH and HNCO + HC(O)H. The calculated results are in qualitative agreement with the observed experimental data. However, CH3ONCO can be produced from the Curtius-type rearrangement route. This is an intriguing finding in this study. Moreover, the effect of one water molecule on the gas-phase pyrolysis of MA has been also explored. We find that the relative energy of the hydrated transition states is effectively lowered when water is added to the reaction. However, the estimated rate constant at 625 K for the naked reaction is about 30 times faster than the reaction with water. Thus, a single water molecule cannot play an important role in the thermal decomposition of MA.

Thiophene oxidation with H2O2 over defect and perfect titanium silicalite-1: a computational study

The oxidation mechanisms of thiophene (Tp) with H2O2 over defect and perfect titanium silicalite-1 (TS-1) were investigated by means of DFT/ONIOM2 calculations for different models 7T:45T, 9T:45T and 13T:45T. The B3LYP, ωB97X-D, and M06-2X functionals were used in the high-level part of ONIOM2, with PM6 in the lower-level part. The related potential energy surface profiles are constructed based on the ωB97X-D/ONIOM2 method for 13T:45T cluster. Four possible paths are proposed for the oxidation of Tp into sulfoxide and sulfoxide into sulfone using H2O2 as an oxidant over defect and perfect TS-1. The dimerization of sulfoxide and sulfone through Diels–Alder cycloaddition is also studied. It is found that perfect TS-1 is highly unfavorable compared to defect TS-1 (TS-d). The calculated activation energy of Tp oxidation with TS-d is found to be remarkably lower than that without any zeolite catalyst. The calculated results may contribute to the understanding of the reaction mechanism of the catalytic oxidative desulfurization of sulfides in liquid fuels.

A Multidimensional B-Spline Correction for Accurate Modeling Sugar Puckering in QM/MM Simulations.

The computational efficiency of approximate quantum mechanical methods allows their use for the construction of multidimensional reaction free energy profiles. It has recently been demonstrated that quantum models based on the neglect of diatomic differential overlap (NNDO) approximation have difficulty modeling deoxyribose and ribose sugar ring puckers and thus limit their predictive value in the study of RNA and DNA systems. A method has been introduced in our previous work to improve the description of the sugar puckering conformational landscape that uses a multidimensional B-spline correction map (BMAP correction) for systems involving intrinsically coupled torsion angles. This method greatly improved the adiabatic potential energy surface profiles of DNA and RNA sugar rings relative to high-level ab initio methods even for highly problematic NDDO-based models. In the present work, a BMAP correction is developed, implemented, and tested in molecular dynamics simulations using the AM1/d-PhoT semiempirical Hamiltonian for biological phosphoryl transfer reactions. Results are presented for gas-phase adiabatic potential energy surfaces of RNA transesterification model reactions and condensed-phase QM/MM free energy surfaces for nonenzymatic and RNase A-catalyzed transesterification reactions. The results show that the BMAP correction is stable, efficient, and leads to improvement in both the potential energy and free energy profiles for the reactions studied, as compared with ab initio and experimental reference data. Exploration of the effect of the size of the quantum mechanical region indicates the best agreement with experimental reaction barriers occurs when the full CpA dinucleotide substrate is treated quantum mechanically with the sugar pucker correction.

Pseudo Jahn–Teller origin of twisting in 3,6-pyridazinedione derivatives; N2C4H2Y2Z2 (Y = O, S, Se, Z = H, F, Cl, Br) compounds

3,6-pyridazinedione and two of its derivatives where oxygen atoms of the molecule are substituted by two sulfur or selenium ( N 2 C 4 Y 2 H 4) were studied with the goal of answering the following question: "Which N 2 C 4 Y 2 H 4 compounds are unstable in their planar configuration?" Additionally, the origin of the twisting instability of 3,6-pyridazinedione planar configuration and three of its 1,2-dihalo derivatives ( N 2 C 4 H 2 O 2 Z 2) were rationalized by employing the pseudo Jahn–Teller effect (PJTE) to explain the difference between N 2 C 4 H 2 O 2 Z 2 structures in series. Therefore, the structures of six 3,6-pyridazinediones ( N 2 C 4 H 2 Y 2 Z 2) were optimized in both equilibrium and planar configurations, and their vibrational frequencies were calculated. Then the adiabatic potential energy surface (APES) profiles along the a2 distortion coordinates were calculated. Based on the calculation results, N 2 C 4 S 2 H 4 and N 2 C 4 Se 2 H 4 compounds were stable in the planar structure; but, due to the vibronic coupling interaction between the 1A1 ground state and the first excited state 1A2, the twisting instability occurred in planar N 2 C 4 H 2 O 2 Z 2 series. The (1 A 1 + 1 A 2) ⊗ a2 problem was found to be the reason of the breaking symmetry phenomena in all the four N 2 C 4 H 2 O 2 Z 2 in series from unstable planar configuration (highest-symmetry C 2v ) to the stable twisted geometry with C 2 symmetry. Finally, the vibronic coupling constants of the PJTE of the compounds in series were estimated by fitting the secular equation roots along the normal coordinates of distortion.

A theoretical study of the thermal Curtius rearrangement of some cinnamoyl azides using the DFT approach

The thermal Curtius rearrangement of cinnamoyl azide, 1-azido-3-phenylprop-2-ene-1-one, and the reactions of some of its derivatives is studied theoretically using the DFT-B3LYP/6-31G(d,p) approach. The potential energy surface profiles of the rearrangement are calculated. The transition state was located and confirmed. The Curtius rearrangement of the studied compounds is a one-stage, discrete reaction. A weak effect of substitution on the reaction rate is due to the unique, localized π system of the studied molecules; strong opposing dipoles span the whole molecule.

Catalytic effect of water, water dimer, or formic acid on the tautomerization of nitroguanidine

We have investigated the reaction mechanisms and kinetics of water, water dimer, or formic acid catalyzed gas-phase isomerization of α-nitroguanidine to β-nitroguanidine by means of high level theoretical methods and transition state theory. The potential energy surface profile has been characterized at the CCSD(T)/6-311++G(2df,2pd)//M06-2X-D3/6-311++G(3df,3pd) level with zero-point energy correction. The calculations indicate that incorporation of water, water dimer, or formic acid molecule into the reactant α-nitroguanidine can noticeably reduce the energy barrier. The reductions are found to be small for water and most significant for formic acid. Most importantly, the kinetics calculations show that the rate constants for the water, water dimer or formic acid assisted reactions are about 14, 14 or 19 orders of magnitude larger than those for the uncatalyzed reaction, respectively. These results suggest that formic acid should play a larger role than both water and water dimer on isomerization of α-nitroguanidine to β-nitroguanidine under tropospheric conditions.

Kinetics and mechanism of the water-assisted reaction of NCO with CH3OH: A quantum chemical study

The mechanism and kinetics of the hydrogen abstraction reaction between the NCO radical and CH3OH without and with one water molecule have been investigated theoretically. The potential energy surface profiles have been constructed at the CCSD(T)/6-311++G(2df,2pd)//BH&HLYP/6-311++G(2df,2pd)+ZPE×0.9335 level. The calculations show that the presence of one water molecule can noticeably reduce the energy barrier. However, the computed rate constants temperatures of 220–600K for the reaction with water is much smaller than that of the naked reaction. We would therefore expect that one water molecule could not play important roles on the NCO+CH3OH reaction in the atmosphere.

Atmospheric Oxidation Mechanism and Kinetic Studies for OH and NO3 Radical-Initiated Reaction of Methyl Methacrylate

The mechanism for OH and NO3 radical-initiated oxidation reactions of methyl methacrylate (MMA) was investigated by using density functional theory (DFT) molecular orbital theory. Geometrical parameters of the reactants, intermediates, transition states, and products were fully optimized at the B3LYP/6-31G(d,p) level. Detailed oxidation pathways were presented and discussed. The rate constants were deduced by the canonical variational transition-state (CVT) theory with the small-curvature tunneling (SCT) correction and the multichannel Rice-Ramspergere-Kassele-Marcus (RRKM) theory, based on the potential energy surface profiles over the general atmospheric temperature range of 180–370 K. The calculated results were in reasonable agreement with experimental measurement.