Molecular Dynamics Simulation of Dissociation Kinetics

The vibrational energy distribution and the degree of dissociation within a system of hydrogen and oxygen molecules was modeled using molecular dynamics (MD). The first step in this process was to model the atomic and molecular interactions. Since hydrogen and oxygen form diatomic molecules, vibration is the only intramolecular force that must be computed. The Morse potential 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. Finally, a system of both hydrogen and oxygen was simulated. The results of this simulation were compared to the CET code and showed excellent agreement. This investigation demonstrated that simple chemical reactions in relatively large systems can be modeled using molecular dynamics. Nomenclature a = acceleration vector Cf = rate constant D = dissociation energy E4 = Morse parameter f = intermolecular force gl = degeneracy H = Hamiltonian k = Boltzmann constant