Mechanistic Study of the Reactions of Methyl Peroxy Radical with Methanol or Hydroxyl Methyl Radical

Abstract

An ab initio and direct dynamic study of the reactions of CHO + CHOH and CHO + CHOH has been carried out over the temperature range of 300-1500 K. All stationary points were calculated at the MP2/aug-cc-pVTZ level of theory for CHO + CHOH or at the M06-2X/MG3S level of theory for CHO + CHOH and identified for the local minimum. The energetic parameters were refined at the QCISD(T)/cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels of theory. For the reaction of CHOO + CHOH, two hydrogen abstraction channels producing CHOOH + CHOH (R1) and CHOOH + CHO (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 an 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 R2 increases dramatically with the increase of the temperature from 500 K. For the reaction of CHOO + CHOH, 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 an excited intermediate followed by its impulsive dissociation was confirmed as the dominant channels with a branching ratio more than 0.99 in the temperature range of 300-1500 K, where products of CHO and OCHOH were given. The rate constant of the dominant channel calculated by multichannel RRKM-VTST is comparable with the available literature data.

Kinetics of the Reactions of Methyl Radical with Hydrogen, Methyl and Ethyl Peroxides

“…The calculated geometries of stationary points for the title reactions are given in Figure S1 (Supporting Information). They are consistent with available values in the literature ( [52] for CH 3 OOH and CH 3 OO; [9] for C 2 H 5 OOH, C 2 H 5 OO, CH 2 CH 2 OOH and CH 3 CH 2 O; [53] for CH 2 O, OH, CH 3 CHO, C 2 H 4 , HOO, CH 3 , CH 4 , CH 3 OH and CH 3 O). Compared to the values calculated at B3LYP and M06‐2X theories, the values calculated at MP2 theory are in good accordance with available literature data and the maximum deviations between them are less than 0.015 Å for the bond lengths and no more than 1.1° for the bond angles.…”

“…The calculated vibrational frequencies of the stationary points for the title reactions are listed in Tables S2a–c (Supporting Information). They are in good agreement with available literature data [9,52–53] . The deviations between the calculated and available literature data are within 5.1 %.…”

Theoretical Study on the Reaction of Nitric Oxide with Propargyl Radical

“…The reaction rate coefficients and branching ratios were computed over a temperature range of 200–800 K and a pressure range of 1.0 × 10 –4 to 10.0 bar with the Mesmer program based on canonical variational transition state theory (CVT) − and Rice–Ramsperger–Kassell–Marcus (RRKM) theory, which has been successfully employed to calculate the individual rate coefficient in the presence of the other channels in multiwell reaction systems. − One-dimensional asymmetric Eckart tunneling corrections were also included.…”

Kinetic Study and Rate Coefficient Calculations of the Reaction of 1-Hydroxyethyl Radical with Nitric Oxide

“…The calculation of rate coefficients and branching ratios of the reaction system was performed using the Mesmer program . As the canonical variational transition state theory (CVT) − and Rice–Ramsperger–Kassel–Marcus (RRKM) theory have been reported to be acceptable in accuracy and are cheap in computational cost for such reaction systems, − they are employed for the rate coefficient calculations with one-dimensional asymmetric Eckart tunneling corrections …”