|$\ell$|-mixing critical densities as a function of the temperature for different principal quantum numbers of hydrogen atoms. Note that the |$\ell$|-changing rates |$q_{\ell \ell ^\prime }$| decrease with the temperature because at higher kinetic energies the time in which the projectile contributes to the Stark mixing is reduced (see fig. 1 in Paper I). This will produce an increase of the critical densities at higher temperatures.