Stimulated Brillouin scattering in a medium with a negative second viscosity

An analysis is made of amplification of sound in a nonequilibrium vibrationally excited gas. It is shown that nonthreshold stimulated Brillouin scattering (STBS) may take place in this medium, the gain and scattering angle depending on the degree of nonequilibrium and on the vibrational relaxation time τ. Specific calculations are made for gas mixtures containing HF and CO₂.