Theoretical study on the OH + CH3NHCOOCH3 reaction
Hui Zhang1, Gui-Ling Zhang, Jing-Yao Liu
1College of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150080, People's Republic of China.
Journal of Computational Chemistry
|December 13, 2007
Summary
The reaction between hydroxyl radical (OH) and methyl N-methylcarbamate (MMC) primarily proceeds via hydrogen abstraction pathways. Calculated rate constants align well with experimental data, providing a reliable model for atmospheric chemistry.
Area of Science:
- Atmospheric Chemistry
- Chemical Kinetics
- Computational Chemistry
Background:
- Methyl N-methylcarbamate (MMC) is an ester with potential relevance in atmospheric chemistry.
- Understanding the reaction pathways of MMC with hydroxyl radicals (OH) is crucial for atmospheric modeling.
- Previous experimental data exists for the total rate constants of this reaction.
Purpose of the Study:
- To investigate the multiple reaction channels of OH + CH3NHC(O)OCH3 using the direct dynamics method.
- To calculate temperature-dependent rate constants for each reaction channel.
- To compare theoretical results with available experimental data.
Main Methods:
- Direct dynamics method employed for reaction mechanism investigation.
- Optimized geometries, frequencies, and minimum energy paths calculated at the MP2/6-311+G(d,p) level.
- Energetic information refined using the BMC-CCSD (single-point) method.
- Rate constants computed via canonical variational transition state theory with small-curvature tunneling correction (200–1000 K).
Main Results:
- Total rate constants show good agreement with experimental data.
- A two-parameter expression for rate constants k(T) = 3.95 x 10(-12) exp(15.41/T) cm3 molecule(-1) s(-1) is provided for 200–1000 K.
- Hydrogen abstraction channels (R1 and R2) identified as major pathways due to lower energy barriers.
- Channels yielding CH3NC(O)OCH3 + H2O and CH3NHC(O)(OH)OCH3 + H2O are minor over the studied temperature range.
Conclusions:
- The direct dynamics calculations accurately predict the reaction kinetics of OH with MMC.
- Hydrogen abstraction is the dominant reaction mechanism under atmospheric conditions.
- The derived rate constant expression can be utilized in atmospheric models for MMC degradation studies.
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