Xiu-Juan Jia

Theoretical Investigation of the Reactions of CF3CHFOCF3 with the OH Radical and Cl Atom

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF(3)CHFOCF(3) (HFE-227 mc) with the OH radical and Cl atom. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the BH&H-LYP/6-311G(d,p) level, and the energetic information along the MEPs is further refined by MC-QCISD theory. The classical energy profile is corrected by the interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunneling effect (SCT) calculated by the variational transition state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k(1) = 2.87 x 10(-21)T(2.80) exp(-1328.60/T) and k(2) = 3.26 x 10(-16)T(1.65) exp(-4642.76/T) cm(3) molecule(-1) s(-1) over the temperature range 220-2000 K. The standard enthalpies of formation for the reactant CF(3)CHFOCF(3) and product radical CF(3)CFOCF(3) are evaluated via group-balanced isodesmic reactions, and the corresponding values are -454.06 +/- 0.2 and -402.74 +/- 0.2 kcal/mol, respectively, evaluated by MC-QCISD theory based on the BH&H-LYP/6-311G(d, p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of formation of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFE-227 mc.

Mechanistic and Kinetic Study of CH2O+O3 Reaction

Both singlet and triplet potential energy surfaces for the reaction of ground-state formaldehyde (CH(2)O) and ozone (O(3)) are theoretically investigated at the BMC-CCSD//BHandHLYP/6-311+G(d,p) level. Various possible isomerization and dissociation pathways are probed. Hydrogen abstraction, oxygen abstraction, and C-addition/elimination are found on both the singlet and the triplet surfaces. The major products for the total reaction are HCO and HOOO, which are generated via hydrogen abstraction. The transition state theory (TST) and multichannel RRKM calculations have been carried out for the total and individual rate constants for determinant channels over a wide range of temperatures and pressures.

Theoretical studies on the mechanisms and dynamics of OH radicals with CH(2)FCF(2)OCHF(2) and CH(2)FOCH(2)F.

The mechanisms and dynamics studies of the multichannel reactions of CH(2)FCF(2)OCHF(2) + OH (R1) and CH(2)FOCH(2)F + OH (R2) have been carried out theoretically. Three hydrogen abstraction channels and two displacement processes are found for reaction R1, whereas there are two hydrogen abstraction channels and one displacement process for reaction R2. The minimum energy paths are optimized at the B3LYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the BMC-QCISD level of theory. By means of canonical variational transition state theory with small-curvature tunneling correction, the rate constants of reactions R1 and R2 are obtained over the temperature range of 220-2000 K. The rate constants are in good agreement with the experimental data for reaction R1 and estimated data for reaction R2. The Arrhenius expression k(1) = 1.62 x 10(-20) T(2.75) exp(-1011/T) for reaction R1 and k(2) = 3.40 x 10(-21) T(3.04) exp(-384/T) for reaction R2 over 220-2000 K are obtained. Furthermore, to further reveal the thermodynamics properties, the enthalpies of formation of reactants CH(2)FCF(2)OCHF(2), CH(2)FOCH(2)F, and the product radicals CHFCF(2)OCHF(2), CH(2)FCF(2)OCF(2), and CHFOCH(2)F are calculated by using isodesmic reactions.

Theoretical study for the reaction of CH3CN with O(P3)

The low-lying triplet and singlet potential energy surfaces of the O((3)P)+CH(3)CN reaction have been studied at the G3(MP2)//B3LYP/6-311+G(d,p) level. On the triplet surface, six kinds of pathways are revealed, namely, direct hydrogen abstraction, C-addition/elimination, N-addition/elimination, substitution, insertion, and H-migration. Multichannel Rice-Ramsperger-Kassel-Marcus theory and transition-state theory are employed to calculate the overall and individual rate constants over a wide range of temperatures and pressures. It is predicted that the direct hydrogen abstraction and C-addition/elimination on triplet potential energy surface are dominant pathways. Major predicted end products include CH(3)+NCO and CH(2)CN+OH. At atmospheric pressure with Ar and N(2) as bath gases, CH(3)C(O)N (IM1) formed by collisional stabilization is dominated at T<700 K, whereas CH(3) and NCO produced by C-addition/elimination pathway are the major products at the temperatures between 800 and 1500 K; the direct hydrogen abstraction leading to CH(2)CN+OH plays an important role at higher temperatures in hydrocarbon combustion chemistry and flames, with estimated contribution of 64% at 2000 K. Furthermore, the calculated rate constants are in good agreement with available experimental data over the temperature range 300-600 K. The kinetic isotope effect has also been calculated for the triplet O((3)P)+CH(3)CN reaction. On the singlet surface, the atomic oxygen can easily insert into C-H or C-C bonds of CH(3)CN, forming the insertion intermediates s-IM8(HOCH(2)CN) and s-IM5(CH(3)OCN) or add to the carbon atom of CN group in CH(3)CN, forming the addition intermediate s-IM1(CH(3)C(O)N); both approaches were found to be barrierless. It is indicated that the singlet reaction exhibits a marked difference from the triplet reaction. This calculation is useful to simulate experimental investigations of the O((3)P)+CH(3)CN reaction in the singlet state surface.

Theoretical study on the kinetics of OH radical reactions with CH3OOH and CH3CH2OOH

The mechanisms and kinetics studies of the OH radical with alkyl hydroperoxides CH3OOH and CH3CH2OOH reactions have been carried out theoretically. The geometries and frequencies of all the stationary points are calculated at the UBHandHLYP/6‐311G(d,p) level, and the energy profiles are further refined by interpolated single‐point energies method at the MC‐QCISD level of theory. For two reactions, five H‐abstraction channels are found and five products (CH3OO, CH2OOH, CH3CH2OO, CH2CH2OOH, and CH3CHOOH) are produced during the above processes. The rate constants for the CH3OOH/CH3CH2OOH + OH reactions are corrected by canonical variational transition state theory within 250–1500 K, and the small‐curvature tunneling is included. The total rate constants are evaluated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained.

Theoretical and kinetic study of the H + C2H5CN reaction

The reaction of H radical with C2H5CN has been studied using various quantum chemistry methods. The geometries were optimized at the B3LYP/6‐311+G(d,p) and B3LYP/6‐311++G(2d,2p) levels. The single‐point energies were calculated using G3 and BMC‐CCSD methods based on B3LYP/6‐311++G(2d,2p) geometries. Four mechanisms were investigated, namely, hydrogen abstraction, C‐addition/elimination, N‐addition/elimination and substitution. The kinetics of this reaction were studied using the transition state theory and multichannel Rice‐Ramsperger‐Kassel‐Marcus methodologies over a wide temperature range of 200–3000 K. The calculated results indicate that C‐addition/elimination channel is the most feasible over the whole temperature range. The deactivation of initial adduct C2H5CHN is dominant at lower temperature with bath gas H2 of 760 Torr; whereas C2H5+HCN is the dominant product at higher temperature. Our calculated rate constants are in good agreement with the available experimental data.

Theoretical study and rate constant calculation for the O(3P) + C2H5CN reaction

The complicated microscopic reaction mechanisms of O(3P) with C2H5CN on the ground electronic state energy surface have been investigated at the G3(MP2) level of theory based on the geometric parameters optimized at the B3LYP/6-311 + G(d, p) level. Two kinds of H-abstraction and addition–elimination channels are considered, namely methylene-H abstraction, methyl-H abstraction, C-addition/elimination and N-addition/elimination. The kinetics of the title reaction have been studied using the TST and multichannel RRKM methodologies over a wide temperature range of 200–2000 K. The results show that the methylene-H abstraction process is predominant for the whole reaction. With an increase of temperature, H-abstraction from the methyl position channel should be taken into account. The C-addition/elimination process provides a few contributions to the title reaction compared with two kinds of H-abstraction channels over the whole temperature region and the N-addition/elimination channel can be negligible due to the high entrance barrier and unstable products.

Computational studies on the mechanism and kinetics of Cl reaction with C2H5I

The dual‐level direct kinetics method has been used to investigate the multichannel reactions of C2H5I + Cl. Three hydrogen abstraction channels and one displacement process are found for the title reaction. The calculation indicates that the hydrogen abstraction from CH2 group is the dominant reaction channel, and the displacement process may be negligible because of the high barrier. The rate constants for individual reaction channels are calculated by the improved canonical variational transition‐state theory with small‐curvature tunneling correction over the temperature range of 220–1500 K. Our results show that the tunneling correction plays an important role in the rate constant calculation in the low‐temperature range. Agreement between the calculated and experimental data available is good. The Arrhenius expression k(T) = 2.33 × 10−16 T1.83 exp(−185.01/T) over a wide temperature range is obtained. Furthermore, the kinetic isotope effects for the reaction C2H5I + Cl are estimated so as to provide theoretical estimation for future laboratory investigation.

THEORETICAL MECHANISTIC STUDY ON THE RADICAL-NEUTRAL REACTION OF CH(X2Π) WITH CH2CO

A theoretical survey on the potential energy surface for the CH (X2Π) + CH2CO reaction has been carried out. The geometries and energies of all stationary points involved in the reaction are calculated at the UB3LYP/6-311+G(d, p) level. And the more accurate energy information is provided by single point calculations at the UCCSD(T)/6-311++G(2d, 2p) level. Relationships of the reactants, transition states, intermediates, and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. Our calculations demonstrate that this reaction is most likely initiated by carbon-to-olefinic carbon attack manners. The results suggest that P1 (C2H3 + CO) is the most important product through two competitive channels R → IM1 → TS1/P1 → P1(C2H3 + CO) and R → IM1 → TS1/6 → IM6 → TS6/P1 → P1(C2H3 + CO). This study presents highlights of the mechanism of the title reaction, which is in good agreement with experimental results.

Mechanistic and kinetic investigations of N2H4 + OH reaction.

The reaction of N2H4 with OH has been investigated by quantum chemical methods. The results show that hydrogen abstraction mechanism is more feasible than substitution mechanism thermodynamically. The calculated rate constants agree with the available experimental data. The calculated results show that the variational effect is small at lower temperature region, while it becomes significant at higher temperature region. On the other hand, the small‐curvature tunneling effect may play an important role in the temperature range 220−3000 K. Moreover, the calculated rate constants show negative temperature dependence at the temperatures below 500 K, which is in accordance with Vaghjianis report that slightly negative temperature dependence is found over the temperature range of 258−637 K. The mechanism of the major product (N2H3) with OH has also been investigated theoretically to understand the title reaction thoroughly.