Coherence, exchange and superelastic electron scattering from sodium

A series of superelastic scattering experiments have been carried out on optically pumped sodium atoms in the 32P3/2 state. The total polarization P+ has been observed at electron energies of 12.1 eV and 22.1 eV referred to the ground state, over a wide range of electron scattering angles. The connections between this parameter, the coherence of the excitation process, and exchange are discussed. Significant departures from P+ = 1 are observed. A qualitative explanation of this phenomenon is described which provides some insight into the collision process. (author)