On the Refractive Index of a Gas under High-Thermal-Nonequilibrium Conditions

An analysis has been made of the influence of the excitation of internal degrees of freedom of molecules on the refractive index (n – 1) under the conditions of high thermal nonequilibrium using the problem on relaxation of molecular nitrogen and oxygen behind the front of a strong shock wave as an example. It has been shown that the processes of vibrational relaxation and the processes of electronic translational relaxation and dissociation alike may exert a substantial influence on the refractive index of the gas. The change in the refractive index has been shown to occur primarily because of the change in the gas density in the course of these processes. Also, it has been found that a slight but detectable influence (about 1–2% for n – 1) on the refractive index is exerted by the change in the polarizability of the gas as a result of the change in vibrational temperatures of the mixture’s molecules and due to the excitation of electronic states and the dissociation of the starting components.