Coherent excitation of Ar 4s(3/2)o1by low energy electrons

Electron-photon coincidence measurements are reported of the excitation of the 4s(3/2) o 1 state of Ar at incident energies of 20 and 30 eV and electron scattering angles up to 80'. Isolation of the 4s(3/2) degrees 1 state was accomplished in the photon channel using a LiF filter. Significant non-zero values of the spin-flip parameter, rho 00 , are reported at both energies as predicted by theory but the level of agreement with available perturbative theories becomes poorer (as might be expected) as the incident electron energy is reduced.