Global potential energy surfaces for O((3)P) + H2O((1)A1) collisions

Area of Science:

• Chemical Physics
• Theoretical Chemistry
• Atmospheric Chemistry

Background:

• Understanding the dynamics of oxygen atom reactions with water is essential for atmospheric chemistry and combustion processes.
• Previous studies lacked comprehensive potential energy surfaces to accurately model these complex interactions.

Purpose of the Study:

• To develop global analytic potential energy surfaces for O((3)P) + H2O((1)A1) collisions.
• To accurately describe the OH + OH hydrogen abstraction and H + OOH hydrogen elimination reaction channels.
• To provide a foundation for quantitative modeling of these collision processes.

Main Methods:

• Ab initio electronic structure calculations using CASSCF + MP2 level with a specific basis set.
• Fitting approximately 10^5 geometries to represent the three lowest triplet adiabatic states.
• Transition state theory rate constant and total cross-section calculations using classical trajectories.

Main Results:

• Developed global analytic potential energy surfaces for O((3)P) + H2O((1)A1) collisions.
• Calculations show good agreement with experimental data for rate constants and cross sections up to 120 kcal/mol.
• Flux-velocity contour maps reveal distinct dynamics and competition between the OH + OH and H + OOH channels.

Conclusions:

• The developed potential energy surfaces accurately represent the O + H2O reaction dynamics.
• Significant differences in surface contributions to reactive channels, especially at higher energies, were identified.
• The surfaces are suitable for quantitative modeling of O + H2O collisions up to 150 kcal/mol.