Molecular Dynamics Simulation of Dissociation Kinetics

The vibrational energy distribution and the degree of dissociation within a system of hydrogen or oxygen molecules were modeled using molecular dynamics. The first step in this process was to model the atomic and molecular interactions. Because hydrogen and oxygen form diatomic molecules, vibration is the only intramolecular force that must be computed. The Morse potential (Morse, P. M., "Diatomic Molecules According to the Wave Mechanics. II. Vibration Levels," Physical Review, Vol. 34, July 1929, pp. 57-64) is used to perform this calculation. Atomic interactions outside the molecule are modeled using the Lennard-Jones potential. The vibrational energy level distribution of this model demonstrated excellent agreement with the Boltzmann distribution. In this molecular dynamics simulation, dissociation occurs when the potential energy between two vibrating atoms exceeds a critical value. Recombination is also possible between two previously dissociated atoms by the reverse mechanism. This process enables a system to start in a state of molecules and proceed to an equilibrated state of atoms and molecules. The molecular dynamics simulation accurately modeled both the rate of dissociation and the ratio of species at equilibrium. This investigation demonstrated that simple chemical reactions in relatively large systems can be modeled using molecular dynamics.