[en] In Na, the energy gap ΔE between the n,d state and the n,l > 2 states is ten times larger than ΔE between n,f and the n,l > 3 states. To investigate the effect of this difference on the d- and f-state l-mixing cross sections, sigma/sub d/ and sigma/sub f/, we have recently carried out experiments to measure sigma/sub d-f/, the l-mixing cross sections for a microwave-induced mixture of d and f states. Using the previously measured values of sigma/sub d/, we have derived values of sigma/sub f/ which have the same n dependence as sigma/sub d/. sigma/sub f/ is larger than sigma/sub d/ for Ne, but smaller for He and Ar. In addition, we have analyzed the final states after one collision with Ar using selective field ionization of the 17l states and have observed that after one collision all the l states are equally populated indicating that there are no Δl selection rules for the process. This confirms the earlier suggestion that l mixing is caused by a short-range interaction