Classical dynamics of state-resolved hyperthermal O((3)P) + H2O((1)A1) collisions.

Area of Science:

• Chemical Physics
• Collision Dynamics
• Theoretical Chemistry

Background:

• Understanding atom-molecule collisions is crucial for atmospheric chemistry and combustion processes.
• Previous studies on O + H2O collisions utilized classical and quantum dynamics on limited potential energy surfaces.

Purpose of the Study:

• To perform classical dynamics calculations for O((3)P) + H2O((1)A1) collisions.
• To investigate product internal energies, ro-vibrationally state-resolved cross sections, and zero-point energy maintenance.
• To model OH formation, H elimination, O-atom exchange, and collisional excitation.

Main Methods:

• Classical dynamics calculations were performed for O + H2O collisions across a range of velocities (2-10 km s(-1)).
• Two potential energy surfaces were employed: a global reactive surface for triplet states and a non-reactive surface.
• Gaussian binning and zero-point maintenance algorithms were used to refine classical trajectory analysis.

Main Results:

• Classical dynamics with specific procedures approximate quantum scattering cross sections for H2O vibrational excitation.
• Without these procedures, classical cross sections significantly overestimate quantum results, particularly for bending modes.
• Reactive surfaces show unusually large product internal excitation at higher velocities, with OOH internal energies reaching 40% of collision energy.

Conclusions:

• Classical dynamics, when appropriately applied, can provide valuable insights into atom-molecule collision dynamics.
• Product internal energy distributions, particularly for OOH, are broad and show high rotational angular momentum.
• The detailed distributions and cross sections serve as a benchmark for future hyperthermal experimental studies.