Ionisation from the sublevels nl with n=5 and 6 in highly charged ions

Coulomb Born-exchange calculations of the scaled or reduced cross section for ionisation from the 4f and all the 5l and 6l sublevels in hydrogenic ions with Z= infinity are made for eight impact electron energies. The results are fitted to a simple function of energy that is readily integrated over a Maxwellian distribution to obtain collision rates. Using these results in prescriptions given in earlier work that include the lowering of the continua in dense plasma one can easily obtain approximate values of cross sections and rates for ionisation from these sublevels in any highly charged ion with finite Z.