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Dual-level direct dynamics studies on the reaction Cl + CHBr(2)Cl
Hui Zhang1, Jia-Yan Wu, Ze-Sheng Li
1Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130061, People's Republic of China.
Journal of Computational Chemistry
|July 27, 2005
Summary
This study investigates the CHBr(2)Cl + Cl reaction using direct dynamics methods. H-abstraction is the dominant pathway at lower temperatures, while Br-abstraction becomes significant at higher temperatures.
Area of Science:
- Chemical Kinetics
- Theoretical Chemistry
- Reaction Dynamics
Background:
- Understanding the reaction mechanisms of halogenated organic compounds is crucial for atmospheric chemistry and environmental science.
- Dichlorobromomethane (CHBr(2)Cl) is a halogenated compound whose reaction with chlorine atoms (Cl) warrants detailed investigation.
- Multichannel reactions involving halogen abstraction present complex kinetic behaviors.
Purpose of the Study:
- To theoretically investigate the multichannel reaction between CHBr(2)Cl and Cl.
- To determine the minimum energy path (MEP) and refine energetic properties for the reaction.
- To calculate and analyze the rate constants for H-, Br-, and Cl-abstraction channels.
Main Methods:
- Direct dynamics methods were employed for theoretical investigations.
- The BH&H-LYP/6-311G(d,p) level was used to obtain the minimum energy path.
- Energetic information was refined using CCSD(T)/6-311+G(2df,2p) single-point calculations.
- Improved Canonical Variational Transition State Theory (ICVT) with Small-Curvature Tunneling (SCT) correction was used to calculate rate constants.
Main Results:
- Theoretical overall rate constants show good agreement with experimental data.
- The overall rate constant is described by k=2.58 x 10(-15) T(1.18) exp(-861.17/T) cm(3)molecule(-1)s(-1) for 200--2400 K.
- H-abstraction is the major channel at lower temperatures.
- Br-abstraction becomes increasingly important as temperature rises, equaling H-abstraction at 2180 K.
- Cl-abstraction is a minor channel across the studied temperature range.
Conclusions:
- The theoretical model accurately predicts the overall reaction rate constants.
- Temperature significantly influences the dominant reaction pathway.
- The relative contributions of H-abstraction and Br-abstraction pathways are temperature-dependent.
- Cl-abstraction plays a minimal role in the overall reaction kinetics.