Jia-yan Wu

Dual-level direct dynamics studies for the reactions of CH3OCH3 and CF3OCH3 with the OH radical

The reactions of CH3OCH3+OH (R1) and CF3OCH3+OH (R2) via two hydrogen abstraction channels are investigated theoretically using the dual-level direct dynamics approach. The minimum energy path calculation is carried out at the MP2/6-311G(d,p) level, and energetic information is further refined by the G3 theory. For each reaction hydrogen abstraction is favored for the out-of-plane hydrogen, while the abstraction from the in-plane hydrogen is a minor channel. Hydrogen-bonded complexes are present on the reactants and products sides of the primary channel, indicating that the reactions may proceed via an indirect mechanism. By means of variational transition state theory with interpolated single-point energies method the dynamic results of all channels are obtained, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants are in good agreement with the experimental data and are fitted to be k1=3.33×10−20 T2.91 exp(−409.7/T) and k2=1.23×...

Theoretical studies on dynamics and thermochemistry of the reactions CF3CHCl2+Cl→CF3CCl2+HCl and CF3CHFCl+Cl→CF3CFCl+HCl

A dual-level direct dynamics study has been carried out for the two hydrogen abstraction reactions CF3CHCl2+Cl and CF3CHFCl+Cl. The geometries and frequencies of the stationary points are optimized at the BHLYP/6-311G(d,p), B3LYP/6-311G(d,p), and MP2/6-31G(d) levels, respectively, with single-point calculations for energy at the BHLYP/6-311++G(3df,2p), G3(MP2), and QCISD(T)/6-311G(d,p) levels. The enthalpies of formation for the species CF3CHCl2, CF3CHFCl, CF3CCl2, and CF3CFCl are evaluated at higher levels. With the information of the potential energy surface at BHLYP/6-311++G(3df,2p)//6-311G(d,p) level, we employ canonical variational transition-state theory with small-curvature tunneling correction to calculate the rate constants. The agreement between theoretical and experimental rate constants is good in the measured temperature range 276–382 K. The effect of fluorine substitution on reactivity of the C–H bond is discussed.

Dual-level direct dynamics studies for the reactions of dimethyl ether with hydrogen atom and methyl radical

The dual‐level direct dynamics approach is employed to study the dynamics of the CH3OCH3 + H (R1) and CH3OCH3 + CH3 (R2) reactions. Low‐level calculations of the potential energy surface are carried out at the MP2/6‐311+G(d,p) level of theory. High‐level energetic information is obtained at the QCISD(T) level of theory with the 6‐311+G(3df,3pd) basis set. The dynamics calculations are performed using variational transition state theory (VTST) with the interpolated single‐point energies (ISPE) method, and small‐curvature tunneling (SCT) is included. It is shown that the reaction of CH3OCH3 with H (R1) may proceed much easier and with a lower barrier height than the reaction with CH3 radical (R2). The calculated rate constants and activation energies are in good agreement with the experimental values. The calculated rate constants are fitted to kR1 = 1.16 × 10−19 T3 exp(−1922/T) and kR2 = 1.66 × 10−28 T5 exp(−3086/T) cm3 mol−1 s−1 over a temperature range 207–2100 K. Furthermore, a small variational effect and large tunneling effect in the lower temperature range are found for the two reactions.

Theoretical study and rate constant calculation of the CH2O+CH3 reaction

The potential energy surface of the CH2O+CH3 reaction is explored at the MP2/6-311++G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single point) levels of theory. Theoretical calculations suggest that the major product channel (R1) is the hydrogen abstraction leading to the product P1 CHO+CH4 (R1), while the addition process leading to P2H+CH3CHO (R2) appears to be negligibly small. The calculated enthalpies and dissociation activation energies for CH3CH2O and CH3OCH2 radicals involved in the reaction are in line with the experimental values. Dual-level dynamics calculation is carried out for the direct hydrogen abstraction channel. The energy profile of (R1) is refined with the interpolated single-point energies (ISPE) method at the QCISD(T)//MP2 level. The rate constants, which are evaluated by canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction, are in good agreement with the available experimental data. It is shown that tunneling effect p...

Dual-level direct dynamics studies on the reaction Cl + CHBr2Cl

Theoretical investigations are carried out on the multichannel reaction CHBr2Cl + Cl by means of direct dynamics methods. The minimum energy path (MEP) is obtained at the BH&H‐LYP/6‐311G(d,p) level, and energetic information is further refined at the CCSD(T)/6‐311+G(2df,2p) (single‐point) level. The rate constants for three reaction channels, H‐abstraction, Br‐abstraction, and Cl‐abstraction, are calculated by using the improved canonical variational transition state theory (ICVT) incorporating with the small‐curvature tunneling (SCT) correction. The theoretical overall rate constants are in good agreement with the available experimental data and are found to be k = 2.58 × 10−15 T1.18 exp(−861.17/T) cm3molecule−1s−1 over the temperature range 200–2400 K. For the title reaction, H‐abstraction reaction channel is the major channel at the lower temperatures, while as the temperature increases, the contribution of Br‐abstraction reaction channel should be taken into account. At 2180 K, the rate constants of these two pathways are equal. Cl‐abstraction reaction channel is minor channel over the whole temperature region.

Direct ab initio dynamics calculations of the reaction rates for the hydrogen abstraction reaction Cl + HC(O)F → HCl + CFO

A direct dynamics method is employed to study the kinetics of the Cl + HC(O)F hydrogen abstraction reaction. The potential energy surface (PES) information is explored from ab initio calculations. Optimized geometries and frequencies of the stationary points as well as the extra points along the minimum energy path (MEP) are calculated at the MP2/6-311+G(d,p) level of theory. In order to improve the energetics along the MEP, single-point calculations are carried out at the QCISD(T)/6-311+G(3df,2p) level of theory. Furthermore, the initial potential information is used to evaluate the rate constants using canonical variational transition-state theory (CVT) with the inclusion of small-curvature tunneling (SCT) corrections over a range of temperatures 220–1500 K. The calculated CVT/SCT rate constants are found to be in good agreement with the available experimental data. Our results show that for the title reaction the variational effect is small at all temperatures, while the tunneling effect plays an important role in the lower temperature range.