Treatment of Thermal Nonequilibrium Dissociation: Theory and Application to H ₂

This work presents a detailed description of the thermochemical nonequilibrium dissociation of diatomic molecules and applies this theory to the case of [Formula: see text] dissociation. In particular, the rovibrational state-specific master equations are analyzed in three key limits/regimes of dissociation-dominated flows: the thermal equilibrium limit, the quasi-steady-state (QSS) regime, and the pre-QSS regime. Under several simplifying assumptions, the macroscopic chemical source term and rovibrational energy expressions that hold in all of these regimes and are ultimately only a function of the translational temperature, [Formula: see text], and the degree of dissociation, [Formula: see text], are proposed. These expressions have two nonequilibrium input parameters: the QSS value in the absence of recombination, i.e., [Formula: see text] for the dissociation rate constant and [Formula: see text] for the rovibrational energy, and a pre-QSS correction factor, [Formula: see text]. Despite their simple functional forms, the proposed expressions are able to reproduce the majority of master equation results for a 0-D isothermal and isochoric reactor for the case of [Formula: see text] dissociation with the third bodies [Formula: see text], H, and He.