Master equation theory for steady-state chemical reactions: Dissociation of diatomic molecules in gases

A steady-state form of the master equation is solved to determine rate constants for dissociation of diatomic molecules. A truncated Morse oscillator model describes the vibrational energies and the (SSH) transition probabilities. Single-quantum vibrational–translational energy exchanges are shown to dominate the rate of dissociation. The theory provides order of magnitude agreement with experimental data for H2, N2, O2, NO, F2, Cl2, Br2, and I2. Anharmonicity of the potential contributes to the lowering of the energy of activation below the bond dissociation energy. Deviations from the Boltzmann distribution cause the energy of activation to decrease at higher temperatures.