Electron-scattering opacity (${\kappa }_{\mathrm{es}}$)

Electron-scattering opacity is approximately independent of density and temperature in a fully ionized nonrelativistic plasma of fixed composition. For hydrogen mass fraction $X$, ${\kappa }_{\mathrm{es}}\simeq 0.2(1+X)\mathrm{c}{\mathrm{m}}^2{\mathrm{g}}^{-1}$.