Thermodynamically Consistent Vibrational-Electron Heating: Generalized Derivation for Excited State Populations

Abstract

Accurate prediction of electron temperature ($T_{\mathrm{e}}$) in non-equilibrium plasma flows is critical for applications ranging from hypersonic flight to plasma-assisted combustion. We recently proposed a thermodynamically consistent model for vibrational-electron (V-e) heating [Phys. Fluids 37, 096141 (2025)] which enforces convergence of $T_{\mathrm{e}}$ to the vibrational temperature ($T_{\mathrm{v}}$) at equilibrium. While the original derivation assumed electron energy loss was dominated by collisions with ground-state molecules, this Letter presents a rigorous generalization of the model. We demonstrate that the heating-to-cooling ratio $\exp (\hat{I}{¸}_{\mathrm{v}}/T_{\mathrm{e}}-\hat{I}{¸}_{\mathrm{v}}/T_{\mathrm{v}})$ with $\hat{I}{¸}_{\mathrm{v}}$ the characteristic vibrational temperature remains valid even when electron cooling interactions with vibrationally excited states are included. This derivation removes the previous constraint assuming ground-state dominance, thereby extending the model's validity to plasma flows where vibrationally excited populations contribute significantly to electron cooling.

4 pages