Direct ab initio dynamics study of the OH + HOCO reaction

Area of Science:

• Chemical kinetics
• Atmospheric chemistry
• Quantum chemistry

Background:

• The hydroxyl radical (OH) is a key species in atmospheric oxidation processes.
• Understanding reactions involving HOCO is crucial for atmospheric modeling.

Purpose of the Study:

• To investigate the reaction mechanism and energetics of OH + HOCO.
• To calculate the thermal rate constant for the OH + HOCO reaction.

Main Methods:

• Coupled-cluster calculations to determine potential energy surfaces.
• Basis set extrapolation to the complete basis set (CBS) limit for accurate energetics.
• Direct dynamics calculations using dual-level ab initio theory.

Main Results:

• The reaction proceeds through an HOC(O)OH intermediate, yielding H2O + CO2.
• Hydrogen bonding significantly impacts the initial reaction stages.
• The rate constant is nearly temperature-independent from 250-800 K, with a predicted value of 1.03 x 10^-11 cm^3 molecule^-1 s^-1 at 300 K.
• A potential small peak in the rate constant was observed between 300-400 K.

Conclusions:

• The OH + HOCO reaction is an important pathway for producing stable molecules in atmospheric systems.
• Computational methods provide accurate insights into reaction dynamics and kinetics.
• The calculated rate constant is valuable for atmospheric chemistry models.