Linear growth rate of the RTI for a partiallyl ionized plasma as a function of perturbation wavenumber k. The dashed line corresponds to the incompressible limit given in Eq. (1). The values ρ₂/ρ₁ = 100, θ = 40, , and ξ_n1 = 10^-6 have been used. Solid lines are calculated with β = 0.1 and dot-dashed lines with β = 0.5, while red lines have a value for the neutral fraction ξ_n2 = 0.9, blue lines ξ_n2 = 0.5, and purple lines ξ_n2 = 0.1.