Ab initio state-specific N₂ + O dissociation and exchange modeling for molecular simulations

Area of Science:

• Chemical Kinetics
• Computational Chemistry
• Atmospheric Chemistry

Background:

• Nitrogen-oxygen reactions are crucial in high-temperature environments like combustion and atmospheric reentry.
• Accurate state-specific reaction rates are needed for modeling these complex systems.
• Previous models often struggle with non-equilibrium conditions and vibrational effects.

Purpose of the Study:

• To compute state-specific cross sections and rates for N2 + O reactions.
• To develop new, compact models (QCT-SSD and QCT-SSE) for dissociation and exchange reactions.
• To validate these models against experimental data and other theoretical approaches.

Main Methods:

• Quasi-classical trajectory (QCT) calculations using ab initio potential energy surfaces.
• Simulation of translational energies up to 23 eV and temperatures from 1000 K to 20,000 K.
• Development of QCT-derived state-specific dissociation (QCT-SSD) and exchange (QCT-SSE) models.

Main Results:

• Vibrational favoring observed for both dissociation and exchange reactions, with higher vibrational states (v=30) showing significantly larger cross sections.
• Exchange reaction exhibits state-dependent activation energy and a cross-section maximum near the dissociation energy.
• The developed QCT-SSD and QCT-SSE models accurately represent over 1 million cross sections with minimal parameters.

Conclusions:

• The new QCT-derived models provide accurate state-specific rates for N2 + O reactions, crucial for computational fluid dynamics and direct simulation Monte Carlo.
• These models outperform existing methods, particularly under non-equilibrium and vibrationally-excited conditions.
• The findings highlight the importance of vibrational state in chemical reaction dynamics for accurate modeling.