Emission and absorption coefficients of diatomic gases in air plasmas produced by Earth entry

Abstract

Accurate radiative properties data are required for the further calculations of radiative transfer in thermodynamic nonequilibrium plasmas produced by Earth entry. However, most of the published radiative properties were determined using the outdated spectroscopic constants, transition probabilities, and partition functions, some of which are less accurate and may deviate from the experimental results. In this paper, the spectral emission and absorption coefficients of diatomic molecules in air plasmas are thoroughly calculated based upon the exact line by line approach. In this scheme, the accurate spectroscopic constants and Franck–Condon factors were selected from the recent publications to reconstruct the rotational structure of spectral lines. Moreover, the level populations were determined by means of our newly reported two-temperature partition functions. The required thermodynamic parameters of each species were obtained by simulating a hypersonic flow field of the RAMC II vehicle. The calculated radiative properties were verified by the experimental and numerical equilibrium radiative source strength and the results show good consistency with measured and theoretical values in the available literature. Based upon the obtained flow field parameters, we finally predicted the distributions of nonequilibrium source strength along the stagnation line. Estimates and analysis were also made for the contributions of each transition system of the diatomic molecule to the total source strength.