‘‘Perfect’’ electron-scattering experiment in sodium

An electron-photon coincidence technique was used to probe the coherence of the excitation of the 3 ${\mathrm{}}^2$P state in sodium by 22.1-eV electrons. The observed coherence implied that spin-dependent interactions could be neglected for forward-angle scattering at this energy. The magnitude and phase of the scattering amplitudes are compared with those derived from experiments which are the time and parity inverse of the present experiments.