Modeling nitric oxide and its dimer: force field development and thermodynamics of dimerization

Area of Science:

• Chemical Physics
• Thermodynamics
• Computational Chemistry

Background:

• Nitric oxide (NO) is a radical that dimerizes to (NO)2 at low temperatures.
• Accurate modeling of NO and (NO)2 behavior is crucial for understanding their chemical and physical properties.

Purpose of the Study:

• To develop and validate an all-atom force field for nitric oxide (NO) and its dimer (NO)2.
• To compute and assess the vapor-liquid equilibrium (VLE) properties of the reactive NO-(NO)2 system.

Main Methods:

• Development of an all-atom force field for NO and (NO)2.
• Continuous Fractional Component Monte Carlo (CFCMC) simulations in a reactive Gibbs ensemble.
• Comparison of simulation results with experimental data and previous force fields.

Main Results:

• The developed force field accurately predicts VLE properties including densities, dimer mole fractions, vapor pressures, and heats of vaporization for the NO-(NO)2 system.
• Simulations demonstrated excellent agreement with experimental data in the temperature range of 120 K to 170 K.
• A parameter study confirmed the influence of force field parameters and (NO)2 partition functions on VLE properties.

Conclusions:

• The new all-atom force field provides a reliable tool for simulating the reactive NO-(NO)2 system.
• The study highlights the importance of accurate force field parameters and molecular partition functions for predicting VLE behavior.
• The validated force field can be used for further investigations into the thermodynamics and phase behavior of nitric oxide systems.