Post-Transition-State Direct Dynamics Simulations on the Ozonolysis of Catechol

Area of Science:

• Atmospheric Chemistry
• Chemical Kinetics
• Computational Chemistry

Background:

• Catechol and ozone reactions are significant in atmospheric chemistry.
• Understanding reaction pathways and product distributions is crucial for atmospheric modeling.

Purpose of the Study:

• To investigate the on-the-fly dynamics of the catechol + ozone reaction.
• To elucidate the post-transition state dynamics and product formation channels.
• To calculate reaction rates and branching ratios for comparison with experimental data.

Main Methods:

• On-the-fly dynamics simulations were performed.
• The PM7 semiempirical method was used to calculate potential energy gradients.
• Hamilton's equations of motion were integrated.
• Calculated results were validated against high-level ab initio methods (B3LYP/6-311+G (2df, 2p)).

Main Results:

• The reaction proceeds via a peroxyacid intermediate, followed by dissociation into various fragments.
• Four major product channels were identified: CO, CO2, H2O, and small carboxylic acid (SCA).
• Reaction rates and product branching ratios were computed at 400 K and 500 K.
• Minimum energy profiles and qualitative activation energies for key channels were determined.

Conclusions:

• The study provides detailed insights into the reaction mechanism and dynamics of catechol + ozone.
• Calculated branching ratios show good agreement with experimental observations.
• The findings contribute to a better understanding of atmospheric oxidation processes involving phenolic compounds.