First-Principle-Inspired Reduced-Order Models of Chemical-Kinetics in $\text{H}_2\left(\text{X}^1\Sigma_g^+\right)$+$\text{H}\left({}^2\text{S}\right)$ System

Abstract

In the present study, two-different reduced-order models are proposed for $\text{H}_2\left(\text{X}^1\Sigma_g^+\right)$+$\text{H}\left({}^2\text{S}\right)$ system by leveraging first-principle quasi-classical trajectory simulations and in-depth master equation analyses. The most recent available ab-initio potential energy surface is adopted to construct a new set of rovibrational state-to-state kinetic database valid over a wide range of temperatures. Firstly, a modified two-temperature model is proposed by incorporating the master equation-informed model parameters, enabling the advanced treatment of the internal energy coupling and the nonequilibrium dissociation predictions. Secondly, a hybrid coarse-graining model is proposed by combining a graph-based approach optimized globally for a wide range of temperatures with a centrifugal-barrier-based coarse-graining method. The proposed reduced-order models offer significantly improved accuracy in predicting the nonequilibrium energy transfer and dissociation dynamics compared to the existing coarse-graining and 2T models in previous studies. In addition, aerothermal heating prediction relevant to Uranus planetary entry reveals 16.5% of convective heat flux discrepancy compared to the present modified 2T approach with the existing 2T, demonstrating the importance of accurate modeling of the chemical-kinetics in the $\text{H}_2\left(\text{X}^1\Sigma_g^+\right)$+$\text{H}\left({}^2\text{S}\right)$ system.