Mechanistic Study of the Reactions of Methyl Peroxy Radical with

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A: Kinetics, Dynamics, Photochemistry, and Excited States

Mechanistic Study of the Reactions of Methyl Peroxy Radical with Methanol or Hydroxyl Methyl Radical Zhongrui Zhao, Jinou Song, Boyang Su, Xiaowen Wang, and Zhijun Li J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b09988 • Publication Date (Web): 17 May 2018 Downloaded from http://pubs.acs.org on May 17, 2018

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The Journal of Physical Chemistry

Mechanistic Study of the Reactions of Methyl Peroxy Radical with Methanol or Hydroxyl Methyl Radical Zhongrui Zhao, Jinou Song *1, Boyang Su, Xiaowen Wang, Zhijun Li State Key Laboratory of Engines, Tianjin University, Tianjin, China, 300072

Abstract An ab initio and direct dynamic study on the reactions of CH3O2 + CH3OH and CH3O2 + CH2OH has been carried out over the temperature range of 300 – 1500 K. All stationary points were calculated at MP2/Aug-cc-pVTZ level of theory for CH3O2 + CH3OH or at M06-2X/MG3S level of theory for CH3O2 + CH2OH and identified for local minimum. The energetic parameters were refined at QCISD (T)/cc-pVTZ and CCSD (T)/aug-cc-pVTZ levels of theory. For the reaction of CH3OO + CH3OH, two hydrogen abstraction channels producing CH3OOH+CH2OH (R1) and CH3OOH+CH3O (R2) were confirmed. These two channels consist of the same reversible first step involving the formation of a prereactive complex in the entrance channel. The rate constants of these two channels have been calculated by canonical transition station theory (TST) and canonical variational transition station theory (VTST) with Eckart tunneling correction, and compared with the available literature data. The positive temperature dependence of the rate constants was observed. The tunneling effect is important at low temperature and decreases with the increase of the temperature. The contribution of R1 to the total rate constant is dominant with branching ratios of 0.93 at 500 K and 0.67 at 1000 K, although the branching ratio for

*

Corresponding author.

E-mail: [email protected] (Jinou Song). 1

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R2 increases dramatically with the increase of the temperature from 500 K. For the reaction of CH3OO + CH2OH, eight channels were explored on the lowest singlet and triplet surfaces and an excited intermediate was found to be formed on the singlet surface. A channel proceeding through the formation of excited intermediate followed by its impulsive dissociation was confirmed as the dominant channels with the branching ratio more than 0.99 at the temperature range of 300 – 1500 K, where products of CH3O and OCH2OH were given. The rate constant of the dominant channel calculated by multichannel RRKM-VTST is comparable with the available literature data.

2


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1. Introduction Alkyl peroxy radicals (ROO) play important roles as reaction intermediates in the atmospheric oxidation1-3 and low-temperature combustion4-5 of every hydrocarbon (RH). They are mainly produced by the reactions of alkyl radicals (R) with molecular oxygen (O2) at low temperature R + O2 – ROO As the temperature increases, the ROO radical becomes thermally unstable and can suffer a number of fates. They can simply dissociate back to form the R and O2, or produce HO2 and the conjugate alkene. The most important successive step of ROO is the isomerization to the hydro-peroxyalkyl radical via internal H atom transfer. The reactions of RO2 with alkanes, which were thought to be the source of chain branching in low temperature oxidation with the formation and decomposition of hydroperoxides,6-7 have been investigated and demonstrated to have a significant impact on predicted ignition times by H. H. Carstensen et.al.8-9 In combustion models the ROO chemistry is important for the low temperature heat release and autoignition. Under tropospheric conditions ROO react with NO, NO2, NO3, HO2, themselves, or other alkyl peroxy radicals, which are responsible for the production of ozone and the tropospheric oxidation of organic species.1-3, 10-12 In the recent past, J. F. Muller et al.13 found the reaction of methyl peroxy radical (CH3OO) with hydroxyl radical (OH) at an unexpectedly high rate and demonstrated this reaction as a major source of atmospheric methanol (CH3OH). CH3OH as a comparatively clean fuel has been used as additives to gasoline or diesel 3



fuel to minimize soot, carbon monoxide and unburned hydrocarbon emissions from engines.14-17 Thus, the reactions of CH3OH with ROO are also important to investigate the behavior of additives presenting high knock resistance properties. C. Anastasi and D. U. Hancock18 made a direct measurement on the reaction of CH3OO + CH3OH and presented a reaction rate constant of 3.2×10-18 cm3molecule-1s-1 at 600 K. Wing Tsang19 suggested an estimated rate constant of 3×10-13 exp(-6900/T) cm3molecule-1s-1 (the uncertainty of factor is 1.3 at 600 K, increasing to 2 at 1000 K) for the reaction of CH3OO + CH3OH → CH2OH + CH3OOH and an estimated rate constant of 2×10-11 cm3molecule-1s-1 with an uncertainty of factor 3 for the reaction of CH3OO + CH2OH → CH3O + OH + HCHO. To the best of our knowledge, the theoretical investigation on the reactions of CH3OO with CH3OH or CH2OH has not been reported to date. Such an investigation will be reported in present article and its results will add useful information to the library of combustion kinetics, especially for the low-temperature oxidation of the mixtures of hydrocarbon and CH3OH. In the experiment on HO2 kinetics in the presence of excess CH3OH, L. E. Christensen and M. Okumura20 found that HO2 formed a complex with CH3OH and relaxed to equilibrium via HO2 + CH3OH = HO2·CH3OH. They measured the equilibrium constant from 231 to 261 K at 50 and 100 Torr and suggested that the HO2·CH3OH complex have a strong hydrogen bond with the hydrogen in HO2 binding to the oxygen in CH3OH. In the rate constant calculations for the reactions of CH3OH + HO2 over the temperature range of 700 – 1300 K, M. Altarawneh et al.21 employed a kinetic scheme as below 4


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CH3OH + HO2 → [Complex of reactants] → Transition state → [Complex of products] → Product + H2O2 S. H. Mousavipour and Z. Homayoon22 investigated theoretically the reactions of CH2OH + HO2 on their lowest singlet and triplet surfaces and found that there exists one deep potential well on the singlet surface which play crucial roles on their kinetics. In the mechanistic study on the reaction of CH3OO + HO2, J. M. Anglada et al.23 reported the results of multireference second-order perturbative energy calculations on both the singlet and triplet surfaces, which show that all the pathways consist of a reversible first step involving the barrierless formation of a hydrogen-bonded prereactive complex in the entrance channel. Prereactive complexes seem to be common and play a key role in all radical - molecule or radical reactions. The investigations in this paper show the presence of one deep potential well on the lowest singlet potential energy surface of CH3OO + CH2OH systems that play crucial roles on its kinetics, and the complexes of reactants and products were also considered for the determination of the height of the energy barrier.

2. Computational Methods Geometries of all of the stationary points were optimized with MP2/Aug-cc-pVTZ theory24 for the reaction of CH3O2 + CH3OH and with M06-2X/MG3S theory25 for the reaction of CH3O2 + CH2OH. Vibrational frequencies and zero-point vibrational energy (ZEP) were calculated at the same theory/basis set combination using the optimized geometries. The results at M06-2X/MG3S level of theory were corrected 5



with a scale factor of 0.972.26 The transition states were subjected to intrinsic reaction coordinate (IRC) calculations27-28 to facilitate connection with minima along the reaction paths. Each IRC terminated upon reaching a minimum using the default criterion. Further refinement in energies for all species was performed using single-point calculations at the QCISD(T)/cc-pVTZ and CCSD(T)/Aug-cc-pVTZ29-30 based on the optimized geometries. For each reaction channel, the minimum energy path (MEP) was calculated in mass-weighted Cartesian coordinates with a gradient step of 0.1 (amu) 1/2boar at CCSD (T)/Aug-cc-pVTZ level of theory. In particular, the single-point energies of reactant and product complexes were calculated with the basis set superposition error (BSSE) correction.31 The Gaussian0932 program was used to optimize the geometries of the stationary points and to calculate their energies. The rate constants for the title reactions were calculated over the temperature 300 1500 K by two methods. One is the multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) and canonical variational transition state theory (VTST) method (RRKM-VTST) by MESMER program33 which has the advantage of calculating the rate constant of each individual step in the presence of the other channels in complex systems and will be used for the channels through the formation of deep potential well. The other is TST or canonical variational transition state theory (VTST) method with the Eckart tunneling correction (TST/Eck or VTST/Eck) by the kISThelp2014 program.34 The one-dimensional Eckart tunneling approximation is reliable and offers similar results to small-curvature tunneling approximation (SCT) for some hydrogen abstraction reactions with less computational cost.35 The partition functions were 6


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calculated by a multiplication of the electronic, translational, vibrational, and rotational partition functions. For the low frequency torsional modes of the reactants and transition states, the one-dimensional (1-D) hindered rotor approximation has been used to calculate their contribution to the partition functions.

3. Results and Discussion 3.1 Potential energy surface and reaction mechanism According to previous investigations and our ab initio results, the following mechanisms (Scheme 1) are suggested for the title reactions. Scheme 1

CH3OO + CH3OH

[vdw]

CH3OO + CH2OH

INT*

CH3OOH + CH2OH

R1

CH3OOH + CH3O

R2

INT

Rw

CH3OOH + cis-CHOH

CH3OOH + CH2O HCOOH + CH3OH CH3O + OCH2OH CH3CH2OH + 1O2 (s) CH3CH2OH + 3O2 (t) CH3OOH + CHOH (t)

R3

R4 R5 Rd R6

R/6 R7

The CH3OO + CH3OH reaction is thought to involve the formation of a van der Waals complex (vdw), which either decomposes back to reactants or rearranges yielding CH3OOH and CH2OH via R1 or yielding CH3OOH and CH3O via R2. For the 7



CH3OO + CH2OH reaction, an excited intermediate (INT*) was found to be formed on the singlet surface without barrier, which may undergo the collisional stabilization (INT) via Rw or dissociate via R3, R4, R5 and Rd. CH3 could transfers from CH3OO to CH2OH via R6 on singlet surface to give CH3CH2OH and singlet 1O2 (s), or via R/6 on triplet surface to give CH3CH2OH and triplet 3O2 (t). In R7 H-atom is abstracted from methyl in CH2OH on triplet surface to produce CH3OOH and triplet CHOH (t). Figure 1 shows the optimized geometries of all the stationary points at the MP2/Aug-cc-pVTZ or M06-2X/MG3S levels of theory along with the available reference data. The geometries calculated in this work compare well with previous results in the literature23 for CH3OO and CH3OOH, in the literature36 for CH3OH, CH3O, HCOOH, CH2O (s) and CH3CH2OH, in the literature37 for 1O2 and 3O2, and in the literature22 for CH2OH. The deviations of all the bond angle and bond length are less than 2.0° and 0.05 ˚A, respectively, which shows a great agreement between the calculated parameters and the available reference data. The natural population analysis (NPA) was performed for complexes and corresponding separated species, and the results were listed in Table S1 (SI 1, Supporting Information). It shows that hydrogen bond plays an important role for the formation of complexes.

[Figure 1.]

Table 1a (for CH3OO + CH3OH) and Table 1b (for CH3OO + CH2OH) list the harmonic vibrational frequencies and zero-point energies (ZPE) calculated at 8


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MP2/Aug-cc-pVTZ or at M06-2X/MG3S levels of theory along with the available experiment data.36 It can be found that the theoretical results are generally greater than the corresponding experimental values, and the average deviations of the calculated frequencies from the experimental data are within 9%, which shows a great agreement between them. The character of each transition state is confirmed by normal mode analysis, which yields one and only one imaginary frequency whose eigenvector corresponds to the direction of each reaction (i.e., 2449 cm-1 for TS1, and 3504 cm-1 for TS2 in Table 1a; 1381 cm-1 for TS3, 1467 cm-1 for TS4, 1541 cm-1 for TS5, 893 cm-1 for TS6, 1181 cm-1 for TS/6, and 1676 cm-1 for TS7 in Table 1b). To determine whether the single reference CCSD(T) method is able to properly describe the energetics of the title reactions, the T1 diagnostic tests38 have been performed for all transition states and intermediate species. The T1 diagnostic values are all less than the threshold value of 0.02 except for channels R3 and R6 (Table 1b). Fortunately, the channels R3 and R6 are less important, which will be illustrated below. Therefore, a single-reference method is expected to give an adequate description of the wave function.

[Table 1a]

[Table 1b]

Tables 2a (for CH3OO + CH3OH) and Table 2b (for CH3OO + CH2OH) list the 9



calculated relative energies (∆E (0 K)) and the relative enthalpies (∆H (298 K)) for all stationary points at the QCISD(T)/cc-pVTZ and CCSD(T)/Aug-cc-pVTZ levels of theory with ZPE corrections included in all the energy differences. The calculated values of ∆H in Tables 2a and 2b are also compared with the corresponding reaction enthalpies evaluated based on the experimental enthalpies of formation39 for species as given in Table 3. For CH3OO radical in particular, an accurate value at 5.30 kcal mol-1 is used.40 Considering the uncertainties in the calculated ∆H values (~1.0 kcal mol-1) and the ∆f H0298 values as given in Table 3, the two sets of data exhibit general consensus.

[Table 2a]

[Table 2b]

[Table 3]

Figures 2a and 2b show the potential energy surfaces (PESs) of the reactions of CH3OO + CH3OH and CH3OO + CH2OH at the CCSD(T)/Aug-cc-pVTZ level of theory. For convenience, the total energy of the reactants was set as zero. As shown in Figure 2a, a stable prereactive complex (vdw) is formed before transition states TS1 and TS2, and its energy is about 3.13 kcal mol-1 lower than the energy of the reactants; the product complexes (vdw1 and vdw2) are also observed, which are about 4.66 (for 10


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R1) and 3.96 (for R2) kcal mol-1 lower than the corresponding separated products. It is found that the barrier height for R1 is 4.08 kcal mol-1 lower than that for R2, indicating that R1 is kinetically more favorable than R2. This finding is much similar to the results of Altarawneh et al.21 in the investigation on the reaction of CH3OH + HO2. These two potential sites could be both kinetically feasible and will be considered in determining the overall rate constant for the reaction CH3OO + CH3OH. As shown in Figure 2b, the reaction of CH3OO + CH2OH forms a excited intermediate INT*, which is 67.41 kcal mol-1 lower than the total energies of CH3OO and CH2OH at the CCSD(T)/Aug-cc-pVTZ level of theory. The intermediate INT* may undergo the collisional stabilization via Rw or dissociate via four possible channels, i.e., R3 with a barrier height of 69.20 kcal mol-1 (TS3), R4 with a barrier height of 43.34 kcal mol-1 (TS4), R5 with a barrier height of 35.53 kcal mol-1 (TS5), and Rd without exit barrier. The product complexes (vdw3, vdw4 and vdw5) were formed along R3, R4 and R5, which are about 6.08 (for R3), 4.64 (for R4) and 7.68 (for R5) kcal mol-1 lower than the corresponding products. The other possible channels on the singlet surface are the impulsive dissociation of INT* (Rd) and the formation of ethanol and singlet molecular oxygen (R6) with a barrier height of 40.39 kcal mol-1 (TS6). On the triplet surface, two channels are found; one is the formation of ethanol and triplet molecular oxygen (R/6) with a barrier height of 225.40 kcal mol-1 (TS/6). The other is a hydrogen transfer reaction (R7) with a barrier height of 20.13 kcal mol-1 (TS7), along which a product complex (vdw7) is formed. This observation indicates that the channels of R6 and R/6 should be kinetically 11



neglectable, while the channel Rd through simple impulsive O-O bond rupture in INT* would be the dominant exit channel because it is favored energetically and entropically over the competing reaction channels that proceed through tight transition states.

[Figure 2a]

[Figure 2b]

3.2 Rate constant calculations Figure 3 shows the classical potential energy curves ( ) and the vibrational adiabatic ground state potential energy curves ( ) as a function of the reaction coordinate (s) at CCSD (T)/Aug-cc-pVTZ//MP2/Aug-cc-pVTZ level of theory for R1, R2 and at CCSD (T)/Aug-cc-pVTZ//M06-2X/MG3S level of theory for R7, where the ground state vibrationally adiabatic potential curve is defined as ( ) = ( ) + ( ). As the reactants are the same for reactions R1 and R2, the values of in Figures 3(a) and 3(b) along the reactants valley show the same trend after the reaction coordinate are extended, where the position of vdw also appeared (Figure S1 in SI 2, Supporting Information). The and curves are similar in shape and the position of the maximum coincides with that of the maximum , which indicates that the variational effect will be small in the calculation of rate constants.41-43 In view of the small variational effect, the TST/Eck method is 12


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employed to calculate the rate constants of R1, R2 and R7. For comparison, the computation with VTST for R1 was also plotted in Figure 4a. A two-step mechanism was assumed for the rate constant calculation of the reaction of CH3OO + CH3OH (SI 3, Supporting Information,). Similar treatment can be found in the work of J. M. Anglada, et al 23. The rate constants of channels through the formation of INT* were calculated with multichannel RRKM-VTST method for the reaction CH3OO + CH2OH. The derived equations of rate constant were given in Supporting Information (SI 4). Since the channels of R6 and R/6 were kinetically neglectable, their rate constants were not calculated in this work. The microcanonical rate coefficient for the impulsive dissociation of INT* was calculated by the canonical variational transition station theory (SI 5, Supporting Information).The RRKM calculations were performed at a bath gas pressure of 1 atm over a temperature range of 300 to 1500 K，He was chosen as bath gas and its Lennard-Jones parameters were set to 11.442 K for epsilon and 2.715 A for sigma as suggested by Jasper et al.44 The collisional energy transfer was described using an exponential down model, and the average energy transferred was assumed to be in a downward direction =CM(T/298) with a value of CM=160 cm-1 for He.45 The Lennard-Jones parameters of INT* was set to 2238 K for epsilon and 4.58 A for sigma according to one-dimensional minimizations.44

[Figure 3]

13



Figures 4a and 4b show the rate constants for reaction systems of CH3OO + CH3OH and CH3OO + CH2OH, and the available reference data.18,19 As shown in Figure 4a, the rate constants of R1 calculated with TST and VTST are similar, indicating that the variational effects are not important. With the Eckart tunneling correction, the calculated rate constants of R1 is in good agreement with the available experimental value18 at 600 K, and comparable with the rate constant estimated by Tsang.19 The rate constants for R1 and R2 have a positive temperature dependence in the calculated temperature range, and the tunneling effect is important only in the low temperature region. The ratios of TST/Eck to TST rate constants are 31.63 and 27.03 at 400 K, 4.58 and 5.92 at 600 K, and 1.30 and 1.50 at 1500 K for R1 and R2, respectively. For the reaction of CH3OO + CH2OH (Figure 4b), Rd is the dominant channel with CH3O and OCH2OH as the major products in the temperature range of 300-1200 K. The calculated rate constant of Rd in this work has a slight negative temperature dependence in the calculated temperature range and is comparable with the rate constant estimated by Tsang19 for the reaction of CH2OH + CH3OO → CH3O + OH + HCHO.

[Figure 4a]

[Figure 4b] The branching ratios have been evaluated and plotted in Figure 5. For the reaction of CH3OO + CH3OH, the contribution of R1 to the total rate constant is dominant with 14


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branching ratios of 0.93 at 500 K and 0.67 at 1000 K, although the branching ratio for R2 increases dramatically with the increase of the temperature from 500 K. For the reaction of CH3OO + CH2OH, the contribution of Rd is dominant with the branching ratio more than 0.99 at the whole calculated temperature range, while the contributions of other channels are negligible.

[Figure 5]

Nonlinear

least-squares

fitting

to

the

calculated

rate

constants

at

the

CCSD(T)/Aug-cc-pVTZ level in Figures 4a and b gives the following rate expressions in cm3 molecule-1 s-1 unit (R = 8.314 J molecule-1 K-1). = 3.421 × 10 . e(!,#/%)

(1)

= 1.318 × 10' (.' e(),'!/%)

(2)

= 2.188 × 10) .# e(',!'/%)

(3)

( = 1.047 × 10( .! e((,((/%)

(4)

) = 3.890 × 10( .'( e((,!/%)

(5)

, = 9.120 × 10 .! e((,#/%)

(6)

- = 1.047 × 10) .#! e(,!'/%)

(7)

' = 2.042 × 10' (.' e(,/%)

(8)

4. Conclusions An ab initio and direct dynamic study on the reactions of CH3O2 + CH3OH and 15



CH3O2 + CH2OH has been carried out over the temperature range of 300 – 1500 K. All stationary points were calculated at MP2/Aug-cc-pVTZ level of theory for CH3O2 + CH3OH or at M06-2X/MG3S level of theory for CH3O2 + CH2OH and identified for local minimum. The energetic parameters were refined at QCISD (T)/cc-pVTZ and CCSD (T)/Aug-cc-pVTZ levels of theory. For the reaction of CH3OO + CH3OH, two hydrogen abstraction channels producing CH3OOH+CH2OH (R1) and CH3OOH+CH3O (R2) were confirmed. These two channels consist of the same reversible first step involving the formation of a prereactive complex in the entrance channel, followed by the irreversible formation of products. The rate constants of these two channels have been calculated with TST and TST/Eck and have positive temperature dependence. The Eckart tunneling effect is only important over the lower temperature region. The contribution of R1 to the total rate constant is dominant with branching ratios of 0.93 at 500 K and 0.67 at 1000 K, although the branching ratio for R2 increases dramatically with the increase of the temperature from 500 K. The calculated rate constant of R1 agree reasonably with the available literature data. For the reaction of CH3OO + CH2OH, eigtht channels were explored on the lowest singlet and triplet surfaces and an excited intermediate was found to be formed on the singlet surface that plays a crucial role in the kinetics. The overall reaction is dominated by a channel proceeding through the formation of excited intermediate on the singlet surface, where CH3O and OCH2OH were given through the impulsive dissociation of the excited intermediate, and its rate constant was calculated by 16


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multichannel RRKM-VTST method. The calculated rate constant of this dominant channel has a slight negative temperature dependence in the calculated temperature range and is comparable with the available literature data for the reaction of CH2OH + CH3OO → CH3O + OH + HCHO.

Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant 51576139 and 51576140. The authors gratefully acknowledge the assistance of Professor Xiaoqing You and Dr. Hongmiao Wang at Tsinghua University for performing rate constant calculations.

References: (1) Lightfoot, P. D.; Cox, R. A.; Crowley, J. N.; Destriau, M.; Hayman, G. D.; Jenkin, M. E.; Moortgat, G. K.; Zabel, F. Organic Peroxy Radicals: Kinetics, Spectroscopy and Tropospheric Chemistry. Atmos. EnViron. 1992, 26, 1805-1961, DOI: 10.1016/0960-1686(92)90423-I. (2) Wallington, T. J.; Dagaut, P.; Kurrylo, M. J. Ultraviolet Absorption Cross Sections and Reaction Kinetics and Mechanisms for Peroxy Radicals in the Gas Phase. Chem. Rev. 1992, 92, 667-710, DOI: 10.1021/cr00012a008. (3) Madronich, S.; Calvert, J. G. Permutation Reactions of Organic Peroxy Radicals in the Troposphere. J. Geophys. Res. Atmos. 1990, 95, 5697-5715, DOI: 10.1029/JD095iD05p05697. (4) Ranzi, E.; Dente, M.; Goldaniga, A.; Bozzano, G.; Faravelli, T. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation and Combustion of 17



Hydrocarbon

Mixtures.

Prog.

Energ.

Combust.

2001,

Page 18 of 35

27,

99-139,

DOI:

10.1016/S0360-1285(00)00013-7 (5) Zador, J.; Taatjes, C. A.; Fernandes, R. X. Kinetics of Elementary Reactions in Low-Temperature Autoignition Chemistry. Prog. Energy. Combust. 2011, 37, 371-421, DOI: 10.1016/j.pecs.2010.06.006. (6) Pollard R. T. In Comprehensive chemical kinetics: Gas-phase Combustion; Bamford C. H., Tipper C. F. H., Eds.; Elsevier: Amsterdam, 1977, Vol. 17. (7) Walker, R.W.; Morley, C. In: Low-temperature Combustion and Autoignition; Pilling M. J., Ed.; Elsevier: Amsterdam, 1997, Vol. 35. (8) Carstensen, H. H.; Dean, A. M. Rate Constants for the Abstraction Reactions RO2 + C2H6; R = H, CH3, and C2H5. P. Combust. Inst. 2005, 30, 995-1003, DOI: 10.1016/j.proci.2004.08.076. (9) Carstensen, H. H.; Dean, A. M.; Deutschmann, O. Rate Constants for the H Abstraction from Alkanes (R–H) by R′O2 Radicals: A Systematic Study on the Impact of R and R′. P. Combust. Inst. 2007, 31, 149-157, DOI: 10.1016/j.proci.2006.08.091. (10) Lightfoot, P. D.; Veyret, B.; Lesclaux, R. Flash Photolysis Study of the CH3O2 + HO2, Reaction between 248 and 573 K. J. Phys. Chem. 1990, 94, 708-714, DOI: 10.1021/j100365a036. (11) Launder, A. M.; Agarwal, J.; Schaefer H.F.III. Exploring Mechanisms of a Tropospheric Archetype: CH3O2 + NO. J. Chem. Phys. 2015, 143, 234302, DOI: 10.1063/1.4937381. (12) Bacak, A.; Bardwell, M. W.; Raventos-Duran, M. T.; Percival, C. J.; Hamer, P. D.; Shallcross, D. E. Kinetics of the CH3O2+NO2 Reaction: A Temperature and Pressure Dependence Study Using Chemical Ionisation Mass Spectrometry. Chem. Phys. Lett. 2006, 419, 125-129, DOI: 10.1016/j.cplett.2005.11.070. 18


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(13) Muller, J. F.; Liu, Z.; Nguyen, V. S.; Stavrakou, T.; Harvey, J. N.; Peeters, J. The Reaction of Methyl Peroxy and Hydroxyl Radicals as a Major Source of Atmospheric Methanol. Nat. Commun. 2016, 7, 13213, DOI: 10.1038/ncomms13213. (14) Agarwal, A. K.; Karare, H.; Dhar, A. Combustion, Performance, Emissions and Particulate Characterization of a Methanol–Gasoline Blend (gasohol) Fuelled Medium Duty Spark Ignition Transportation

Engine.

Fuel.

Process.

Technol.

2014,

121,

16-24,

DOI:

10.1016/j.fuproc.2013.12.014. (15) Balki, M. K.; Sayin, C.; Canakci, M. The Effect of Different Alcohol Fuels on the Performance, Emission and Combustion Characteristics of a Gasoline Engine. Fuel 2014, 115, 901-906, DOI: 10.1016/j.fuel.2012.09.020. (16) Huang, Z. H.; Lu, H. B.; Jiang, D. M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang, X. B.; Engine Performance and Emissions of a Compression Ignition Engine Operating on the Diesel/Methanol Blends. Proc. Instn Mech. Engrs Part D: J. Automobile Engineering, 2004, 218, 435-447, DOI: 10.1243/095440704773599944 (17) Huang, Z. H.; Lu, H. B.; Jiang, D. M.; Zeng, K.; Liu, B.; Zhang, J. Q.; Wang, X. B. Combustion Behaviors of a Compression Ignition Engine Fuelled with Diesel/Methanol Blends under Various Fuel Delivery Advance Angles. Bioresour. Technol. 2004, 95, 331-341, DOI: 10.1016/j.biortech.2004.02.018 (18) Anastasi, C.; Hancock, D. U. Reaction of Methylperoxy Radicals with Methanol and Formaldehyde at 600 K. J. Chem. Soc. Faraday Trans. 1984, 80, 935-939, DOI: 10.1039/f19848000935. (19) Tsang, W. Chemical Kinetic Data Base for Combustion Chemistry. Part 2. Methanol. J. Phys. Chem. Ref. Data. 1987, 16, 471-508, DOI: 10.1063/1.555802. 19



(20) Christensen, L. E.; Okumura, M.; Hansen, J. C.; Sander, S. P.; Francisco. J. S. Experimental and Ab Initio Study of the HO2.CH3OH Complex: Thermodynamics and Kinetics of Formation. J. Phys. Chem. A 2006, 110, 6948-6959, DOI: 10.1021/jp056579a. (21) Altarawneh, M.; Al-Muhtaseb, A. H.; Dlugogorski, B. Z.; Kennedy, E. M.; Mackie, J. C. Rate Constants for Hydrogen Abstraction Reactions by the Hydroperoxyl Radical from Methanol, Ethenol, Acetaldehyde, Toluene, and Phenol. J. Comput. Chem. 2011, 32, 1725-1733, DOI: 10.1002/jcc.21756. (22) Mousavipour, S. H.; Homayoon, Z. Multichannel RRKM-TST and CVT Rate Constant Calculations for Reactions of CH2OH or CH3O with HO2. J. Phys. Chem. A 2011, 115, 3291-3300, DOI: 10.1021/jp112081r. (23) Anglada, J. M.; Olivella, S.; Sole, A. Mechanistic Study of the CH3O2• + HO2•→CH3O2H + O2 Reaction in the Gas Phase. Computational Evidence for the Formation of a Hydrogen-Bonded Diradical Complex. J. Phys. Chem. A. 2006, 110, 6073-6082, DOI: 10.1021/jp060798u. (24) Møller, C.; Plesset, M. S. Note on an Approximation Treatment for Many- Electron Systems. Phys. Rev. 1934, 46, 618-622, DOI: 10.1103/PhysRev.46.618. (25) Zhao, Y.; Truhlar, D.G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215–241. DOI: 10.1007/s00214-007-0310-x. (26) Alecu, I. M.; Zheng, J.; Zhao, Y.; Truhlar, D. G. Computational Thermochemistry: Scale Factor Databases and Scale Factors for Vibrational Frequencies Obtained from Electronic Model Chemistries. J. Chem. Theory. Comput. 2010, 6, 2872-2887, DOI: 10.1021/ct100326h. 20


Page 20 of 35

Page 21 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(27) Gonzales, C.; Schlegel, H. B. An Improved Algorithm for Reaction Path Following. J. Chem. Phys. 1989, 90, 2154-2061, DOI: 10.1063/1.456010. (28) Gonzales, C.; Schlegel, H. B. Reaction Path Following in Mass-Weighted Internal Coordinates. J. Phys. Chem. 1990, 94, 5523-5527, DOI: 10.1021/j100377a021. (29) Scuseria, G. E.; Schaefer III H. F. Is Coupled Cluster Singles and Doubles (CCSD) More Computationally Intensive than Quadratic Configuration Interaction (QCISD)? J. Chem. Phys. 1989, 90, 3700-3703, DOI: 10.1063/1.455827. (30) Pople, J. A.; Head-Gordon, M.; Raghavachari, K. Quadratic Configuration Interaction. A General Technique for Determining Electron Correlation Energies. J. Chem. Phys. 1987, 87, 5968-5975, DOI: 10.1063/1.453520. (31) Simon, S.; Duran, M.; Dannenberg, J. J. How Does Basis Set Superposition Error Change the Potential Surfaces for Hydrogen-Bonded Dimers? J. Chem. Phys. 1996, 105, 11024-11031, DOI: 10.1063/1.472902. (32) Frisch, M. J.; W.Trucks, G.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A. et al. Gaussian 09, Version 7.0, Gaussian, Inc., Wallingford, CT, 2009. (33) Robertson, S. H.; Glowacki, D. R.; Liang, C. H.; Morley, C. M.; Pilling Michael, J. MESMER, An Object-oriented Ctt Program for Carrying Out ME Calculations and Eigenvalue-eigenvector Analysis on Arbitrary Multiple Well Systems; Available for download on SourceForge: http://sourceforge.net/projects/mesmer/ . (34) Canneaux, S.; Bohr, F.; Henon, E. KiSThelP: A Program to Predict Thermodynamic Properties and Rate Constants from Quantum Chemistry Results. J. Comput. Chem. 2014, 35, 21



Page 22 of 35

82-93, DOI: 10.1002/jcc.23470. (35) Li, X. Y.; You, X. Q.; Law, C. K.; Truhlar, D. G. Kinetics and Branching Fractions of the Hydrogen Abstraction Reaction from Methyl Butenoates by H Atoms, Phys. Chem. Chem. Phys. 2017, 19, 16563-16575, DOI: 10.1039/c7cp01686g. (36) NIST Computational Chemistry Comparison and Benchmark Database. Release 18 (October 2016). http://cccbdb.nist.gov/. (37) Herzberg, G. Spectra of Diatomic Molecules, 2nd ed.; McGraw-Hill: New York, 1950. (38) Lee, T. J.; Taylor, P. R. A Diagnostic for Determining the Quality of Single-Reference Electron

Correlation

Methods.

Int.

J.

Quantum

Chem.

1989,

36,

199-207,

DOI:

10.1002/qua.560360824. (39) NIST Chemistry Webbook Standard Reference Database, Number 69, (February 2015). http://webbook.nist.gov. (40) Resende, S. M.; De Almeida, W. B. Thermodynamical Analysis of the Atmospheric Fate of the

CH3SCH2O2

Radical.

Phys.

Chem.

Chem.

Phys.

1999,

1,

2953-2959,

DOI:

10.1039/A902423I. (41) Liu, J. Y.; Li, Z. S.; Wu, J. Y.; Wei, Z. G.; Zhang, G.; Sun, C. C. Theoretical Study and Rate Constant Calculation of the CH2O+CH3 Reaction. J. Chem. Phys. 2003, 119, 7214-7221, DOI: 10.1063/1.1605938. (42) Chen, C. X.; Song, J. O.; Song, C. L.; Lv, G.; Li, Z. J. Ab Initio and Direct Dynamics Study on

the

C2H3+CH3CH2OH

Reaction.

Mol.

Phys.

2016,

114,

315-324,

DOI:

10.1080/00268976.2015.1102347. (43) Chen, C. X.; Song, J. O.; Song, C. L.; Lv, G.; Li, Z. J. Ab Initio and Direct Dynamics Study 22


Page 23 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


on the Hydrogen Abstraction Reaction C2H3+CH3CHO. Comput. Theor. Chem. 2016, 1075, 63-69, DOI: 10.1016/j.comptc.2015.11.018. (44) Jasper, A. W.; Miller, J. A. Lennard–Jones Parameters for Combustion and Chemical Kinetics Modeling from Full-Dimensional Intermolecular Potentials. Combust. Flame. 2014, 161, 101-110, DOI: 10.1016/j.combustflame.2013.08.004. http://tcg.cse.anl.gov/papr/databases/transport.dat (45) Carr, S. A.; Glowacki, D. R.; Liang, C. H.; Baeza-Romero, M. T.; Blitz, M. A.; Pilling, M. J.; Seakins, P. W. Experimental and Modeling Studies of the Pressure and Temperature Dependences of the Kinetics and the OH Yields in the Acetyl+O2 Reaction. J. Phys. Chem. A, 2011, 115, 1069-1085, DOI: 10.1021/jp1099199.

23



Page 24 of 35

Tables Table 1a. Theoretical and experimental harmonic vibrational frequencies (cm-1), ZPE (kcal mol-1) and the T1 diagnostic values in CH3OO + CH3OH system at MP2/Aug-cc-pVTZ and M06-2X/MG3S levels of theory. Species

Methods

Frequencies

ZPE

CH3OH

MP2

3859,3183,3126,3055,1532,1517,1492,1380,1195,1095,1074, 289

32.74

M062X

3930,3133,3085,3029,1522,1505,1488,1375,1182,1117,1073,344

31.67

Expt CH3O2

3232,3218,3105,1511,1495,1465,1282,1211,1157,962,510, 131

27.59

M062X

3179,3178,3078,1494,1461,1304,1202,1146,983,513,110

26.59

3033,3020,2954,1453,1441,1408,1183,1117,902, 482,170 3857,3334,3181,1518,1380,1218,1079,625,433

23.97

M062X

3920,3287,3151,1496,1362,1239,1064,577,414

22.95

a

3650,1459,1334,1176,1048,482,234

MP2

3134,3098,3014,1544,1429,1423,1132,982,809

23.69

M062X

3085,3041,2969,1520,1395,1388,1137,970,889

22.79

Expt CH3O2H

a

MP2

Expt CH3O

3681,3000,2960,2844,1477,1477,1455,1345,1165,1060,1033, 200

MP2

Expt CH2OH

a

a

MP2

T1 diag

2840,2758,1412,1047,914,652 3838,3191,3157,3068,1535,1485,1476,1377,1213,1193,1073,860,

34.87

452, 266,204 M062X

3845,3148,3128,3052,1519,1480,1463,1415,1228,1185,1119,958,

33.78

470,262,213 vdw

MP2

3842,3240,3227,3183,3124,3110,3053,1534,1518,1515,1506,1498,

61.51

0.0171

58.55

0.0183

57.38

0.0196

60.61

0.0119

60.07

0.0076

1488,1412,1339,1211,1196,1152,1124,1088,945,518,502,179,151, 114,93,71,53,24 TS1

MP2

3841,3217,3197,3179,3090,3078,1615,1520,1505,1492,1478,1404, 1318,1235,1216,1190,1181,1166,1112,986,658,502,477,372,344, 211,144,121,91,2449i

TS2

MP2

3198,3170,3142,3093,3072,3019,1533,1529,1498,1485,1472,1459, 1426,1227,1208,1189,1125,1108,1072,996,930,665,475,328,225, 169,149,99,63,3504i

vdw1

MP2

3745,3713,3316,3194,3173,3162,3076,1534,1521,1488,1479,1458, 1428,1236,1218,1197,1131,1067,863,787,722,457,347,287,254, 180,125,108,78,39

vdw2

MP2

3695,3184,3158,3154,3107,3065,3015,1539,1533,1486,1476,1462, 1445,1413,1221,1194,1160,1081,1045,864,861,557,455,273,181, 137,89, 78,45,37

a

Ref. 36.

24


Page 25 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1b. Theoretical and experimental harmonic vibrational frequencies (cm-1), ZPE (kcal mol-1) and the T1 diagnostic values in CH3OO + CH2OH system at the M06-2X/MG3S level of theory. Species

Methods

Frequencies

ZPE

CH2O

M062X

3042,2970,1875,1540,1275,1216

16.57

Expt

a

2834,2782,1746,1500,1167, 1249

cis-CHOH

M062X

3672,2870,1483,1382,1249,1018

16.23

HCOOH

M062X

3813,3116,1871,1410,1316,1159,1072,674,646

20.96

Expta

3570,2943,1770,1387,1229,1105,1033,638,625

M062X

1716

1

O2(s)

Expt CH3CH2OH

a

M062X

T1 diag

2.46

1484 3907,3133,3120,3099,3042,3031,1526,1500,1493,1429,1403,1378,

49.16

1283,1154,1112,1069,905,801,426,297,254 a

Expt

3653,2991,2984,2939,2910,2900,1490,1464,1446,1412,1371,1275, 1256,1161,1091,1028,888,812,417

CHOH(t)

M062X

3790,3152,1329,1175,1090,388

15.27

3

M062X

1771

2.46

O2(t)

a

Expt

1580

INT

M062X

3891,3148,3122,3119,3058,3045,1547,1520,1480,1459,1439,1391,

TS3

M062X

3759,3138,3122,3115,3041,2027,1538,1521,1480,1460,1445,1353,

54.88

0.0112

50.46

0.0223

50.89

0.0172

49.67

0.0175

50.96

0.0431

50.44

0.0166

47.77

0.0194

52.05

0.0152

52.54

0.0135

54.03

0.0139

51.07

0.0155

1248,1234,1195,1182,1130,1096,1059,978,540,451,425,324,208,111, 72

1231,1217,1186,1126,1039,957,693,518,462,285,229,160,122,71,1381i TS4

M062X

3156,3137,3114,3055,3044,2065,1595,1522,1476,1462,1409,1308, 1272,1223,1196,1182,1114,1001,920,688,566,395,330,197,126,52, 1476i

TS5

M062X

3876,3113,3068,3063,3008,1777,1513,1456,1442,1406,1300,1260, 1200,1183,1151,1078,1046,1002,672,589,461,328,313,197,125,103, 1541i

TS6

M062X

3880,3264,3258,3208,3139,3055,1524,1415,1393,1386,1280,1244,

TS/6

M062X

3897,3287,3381,3240,3108,3098,1507,1393,1385,1373,1359,1213,

1190,1135,1108,1050,1005,764,529,473,395,309,277,143, 138,92,893i

1149,1114,1109,1092,1006,665,490,388,356,252,179,153,123,72,1181i TS7

M062X

3669,3199,3164,3132,30050,1597,1510,1481,1461,1342,1317,1226, 1184,1128,1079,974,819,630,497,488,415,337,240,198,122,102,1676i

vdw3

M062X

3698,3496,3151,3109,3032,2912,1523,1511,1478,1473,1460,1403,

vdw4

M062X

3673,3156,3120,3099,3046,3005,1850,1541,1523,1494,1480,1467,

1255,1231,1181,1119,1024,959,663,474,399,268,220,175, 89,73,65

1290,1237,1232,1189,1124,960,630,477,287,247,221,170,134,88,55 vdw5

M062X

3920,3421,3174,3132,3110,3063,1842,1524,1522,1492,1452,1405, 1362,1243,1193,1089,1086,1077,899,699,305,216,186,165, 122,121,43

vdw7

M062X

3659,3605,3160,3137,3134,3055,1519,1484,1468,1461,1365,1268,

OCH2OH

M062X

3893,3011,2897,1413,1356,1307,1165,1130,1018,763,560,294

1233,1193,1115,1093,958,633,479,445,297,264,219,195,151,91,56

a

Ref. 36.

25


26.14


Page 26 of 35

Table 2a. Theoretical and experimental relative energies of various species in CH3OO + CH3OH system at the QCISD(T)/cc-pVTZ and CCSD(T)/ Aug-cc-pVTZ levels of theory ∆E(0 K) (kcal mol-1)

Species

CCSD(T)

∆H(298 K) (kcal mol-1)

QCISD(T)

CCSD(T)

a

Expt

QCISD(Tt)

CH3OH+CH3O2

0.00

0.00

0.00

0.00

vdw

-3.13

-3.13

-2.78

-2.78

TS1

15.16

14.94

14.44

14.22

vdw1

5.62

5.75

5.79

5.92

CH2OH+CH3O2H

10.28

10.44

10.52

10.67

TS2

19.24

19.00

18.64

18.40

vdw2

14.37

14.28

14.62

14.53

CH3O+CH3O2H

18.33

18.52

18.38

18.58

0.00

10.25(±2.39)

16.47

All values are relative to the separated reactants. a Enthalpies of reactions calculated from (∆f H0298) values of the species given in Table 3. Table 2b. Theoretical and experimental relative energies of various species in CH3OO + CH2OH system at the QCISD(T)/cc-pVTZ and CCSD(T)/ Aug-cc-pVTZ levels of theory ∆E(0 K) (kcal mol-1)

Species

∆H(298 K) (kcal mol-1)

CCSD(T)

QCISD(T)

CCSD(T)

QCISD(T)

CH3O2+CH2OH

0.00

0.00

0.00

0.00

INT

-67.41

-66.78

-68.59

-67.96

TS3

1.79

1.99

0.87

1.72

vdw3

-4.65

-3.83

-4.98

-4.16

CH3O2H+cis-CHOH

1.43

1.44

1.04

1.06

TS4

-24.07

-23.64

-25.33

-24.89

vdw4

-58.86

-58.21

-59.16

-58.51

CH3O2H+CH2O

-54.22

-54.47

-54.63

-54.88

TS5

-27.03

-25.78

-28.14

-26.89

vdw5

-142.97

-142.30

-143.36

-142.69

HCOOH+CH3OH

-135.29

-126.50

-135.76

-126.97

TS6

40.39

43.03

39.56

42.70

CH3CH2OH+1O2(s)

-24.13

-24.76

-24.49

-25.13

TS/6

225.40

225.31

224.84

224.63

3

CH3CH2OH+ O2(t)

-54.55

-55.50

-54.91

-55.86

TS7

20.13

20.22

19.31

19.40

vdw7

15.89

17.02

15.70

16.83

CH3O2H+CHOH(t)

27.90

22.04

27.70

21.84

CH3O+OCH2OH

-35.03

-34.71

-35.41

-35.09

Expt

a

0.00

-60.46

-142.69

-59.24

All values are relative to the separated reactants. a Enthalpies of reactions calculated from (∆f H0298) values of the species given in Table 3. 26


Page 27 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 3. Experimental enthalpies of formation (∆f H0298). 8fH°(298 K) (kcal mol-1)

Species CH3O2

a

5.30 b

-49.04±2.39

b

-2.15±0.96

CH3OH CH2OH

b

-31.34

CH3O2H b

4.07±0.96

CH3O

b

CH3CH2OH

-56.09

b

-25.97

CH2O

b

HCOOH 3

O2(t)

a b

b

-90.50 0.00

Ref. 40. Ref. 39.

27



Figures

.0 9

{1

{1

4}

4}

0 {1.4

.39 0}

87 } 1.0 090 . {1

7 08 } 1. 090 . 1 {

34 1 .4 4 7 } 4 {1 . 4 5 6 ] [ 1.

5 29 } 1. 295 ] . 5 {1 .33 [1

86 1.0 089} ] . {1 .079 [1

{1 . 2 09 }

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 35

28


Page 29 of 35

H2

H9 H8

1.0

09 1 .4

95

C7

1. 2 65

1.160 12 1. 0

78.2

1.3

34

H11

TS4

2 09 1.

H3

8 41

105.2 109.9

O5 106.5

C1

O10 379 113.3 1. 109.0

C 21 7 107.8 04 105.6 1 110.1

O6

109.9

1 09 1.

H9 11 1.4

H11

H8

H4

INT

6

29


1.090

1.4 15

110.7

113.4

O10

H2

O5

O6

120.2

119.3

1.292

1.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


C1

110.2

0 09 110.3 1.

H3

H4

1.1

91 1.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

00


Figure 1. Optimized geometries of the stationary points (bond lengths in angstroms (˚A) and angles in degrees (°)) at the M06-2X/MG3S level and at MP2/Aug-cc-pVTZ level (the results in braces). The values in parentheses are the corresponding experimental values36,37 and those in the square brackets are the corresponding values calculated from references.22, 23

30


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25

∆E(kcal mol-1 ) TS2 19.24

20

CH3O+CH 3O2H 18.33

TS1 15.16

15

vdw2 14.37 CH2OH+CH3O2H 10.28

10 vdw1 5.62

5

0

CH3OH+CH3O2 vdw -3.13

-5

Figure 2a. Relative energies of the stationary points of CH3OO + CH3OH system ( kcal mol-1) at the CCSD (T)/Aug-cc-pVTZ level.

-1 40 ∆E(kcal mol )

TS6 40.39

20 0

TS3 1.79 CH2OH+CH3O2

CH3O2H+cis-CHOH 1.43

vdw3 -4.65

1

-20

CH3CH2OH+ O2(s) TS4 -24.07 -24.13

-40

TS5 -31.88

CH3O+OCH2OH -35.03

INT -67.41

-60

CH3O2H+CH2O vdw4 -58.86

-54.22

-80 -100 -120

HCOOH+CH3OH vdw5 -142.97

Singlet

-140

-135.29

250 ∆E(kcal mol-1 ) TS/6 225.40

200 CH3O2H+CHOH(t) 27.90

TS7 20.13

0

vdw7 15.89

CH2OH+CH3O2

CH3CH2OH+3O2(t)

-50

-54.55

Triplet

Figure 2b. Relative energies of the stationary points of CH3OO + CH2OH system ( kcal mol-1) on both singlet and triplet surfaces at the CCSD(T)/Aug-cc-pVTZ level. 31



ZPE

60

60

ZPE 50

50

E(kcal mol-1)

VGa

E(kcal.mol-1)

VGa

40

40

0

VMEP

0

VMEP

-10

-10 -20 -20 -2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

s((amu)1/2bohr)

1.5

2.0

-2.0

-1.5

-1.0

-0.5

0.0

0.5

S((amu)1/2bohr)

(a) R1

1.0

1.5

2.0

(b) R2 50

ZPE 40

E(kcal mol-1)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 35

VGa

0

VMEP

-10

-20 -1.5

-1.0

-0.5

0.0

0.5

S((amu)1/2bohr)

1.0

1.5

(c) R7 Figure 3. The classical potential energy (VMEP) and the vibrational adiabatic ground state potential energy ( ) curves as a function of the reaction coordinate (s) ((amu)1/2bohr) at CCSD (T)/Aug-cc-pVTZ//MP2/Aug-cc-pVTZ level of theory for the reaction R1, R2 and at CCSD (T)/Aug-cc-pVTZ//M06-2X/MG3S level of theory for the reaction R7.

32


Page 33 of 35

-12 -14

log [k(cm3molecule-1s-1)]

-16 -18 -20 -22 -24 -26 -28 0.5

1.0

1.5

2.0

2.5

3.0

3.5

-1

1000/T(K )

Figure 4a Rate constants for reaction of CH3OO + CH3OH over the temperature range 300-1500 K (blue line, Ref. 19; blue rhombus, Ref. 18; black line, R1; red line, R2; solid lines, with TST/Eck; dashed lines, with TST; dash-dot line, with VTST).

-10

log [k(cm3/molecule/s)]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-15

-20

-25

-30 0.5

1.0

1.5

2.0

2.5

3.0

3.5

1000/T(K-1)

Figure 4b Rate constants for reaction CH3OO + CH2OH over the temperature range 300-1500 K (green line, R3; light-magenta line, R4; light-cyan line, Rw; black line, R5; dark yellow, Rd; red line, R7; blue line, Ref. 19).

33



1.0

R1

Branching ratio

0.8

0.6

0.4

0.2

R2 0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

-1

1000/T (K )

(a) CH3OH+CH3O2.

1.0

0.8

Branching ratio

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

R3 R4 R5 Rw R7 Rd

0.6

0.4

0.2

0.0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

1000/T (K-1)

(b) CH2OH+CH3O2. Figure 5 Branching ratios over the temperature range of 300-1500 K

34


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TOC Graphic

1.43

1.79

0.00

+

-4.65 -24.07 -31.88

+

-67.41

+ -35.03 -58.86

-54.22 +

+ -135.29 -142.97

35


Mechanistic Study of the Reactions of Methyl Peroxy Radical with

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