Light scattering and sound propagation in a chemically reacting binary gas mixture

The aim of this paper is to study time-dependent problems like sound propagation and light scattering in binary mixtures undergoing a simple reversible symmetric reaction—of the type A+A⇌B+B—close to the final stage of the chemical reaction where the system tends to chemical equilibrium. The molecules of the gas are modeled as rigid spheres and—apart from the binding (or formation) energy of the molecules—the internal degrees of freedom were not taken into account. The hydrodynamic description is based on the conservation laws of mass, momentum and energy closed by the constitutive equations for the pressure tensor, heat flux vector, diffusion velocity and rate of reaction which correspond to the Navier–Stokes law and generalized laws of Fourier, Fick and Arrhenius, respectively. For the problem of sound propagation it is shown how endothermic and exothermic reactions have influence on the phase speed and on the attenuation coefficient, whereas for the problem of light scattering, their influences on the width of the Rayleigh and Brillouin lines and the position of the Brillouin peak are analyzed.