Absolute elastic differential cross sections of electrons scattered by 3P3/22sodium

We demonstrate a procedure to obtain absolute differential cross sections for electron scattering by excited atoms. Specifically we report on electron scattering by ground-state and laser-excited 3 ${}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{}$, F=3 sodium using an electron and photon double-recoil technique. Measured differential cross sections are obtained with 3-eV electrons in the angular range from 25° to 40°. Agreement of the ground-state scattering data with a four-state exchange close-coupling calculation [D. L. Moores and D. W. Norcross, J. Phys. B 5, 1482 (1972)] is to within experimental error. Cross sections for excited-state atoms are four to ten times larger than those for ground-state atoms. There are at present no theoretical data for comparison.