Resonance structures in the cross section for free-free radiative transitions in e--Ne and e--Ar scattering

Using an electron spectrometer and a CW CO 2 laser the author has measured free-free transitions influenced by scattering resonances. The author has measured this effect in the case of the p-wave neon and argon resonances around 16.1 and 11.1 eV respectively. Resonance structures have been obtained at scattering angles of 20 and 160 degrees for neon and 20, 30 and 50 degrees for argon. The measurements were compared with calculations based on the soft-photon approximation for free-free transitions and on the Fano formalism for the description of the resonances. In the case of neon the agreement is very good whereas in the case of argon a high non-resonant background in the free-free scattering at small angles occurs which is not predicted by the soft-photon approximation.