Electron excitation of Na(3S) and Na(3P) atoms to the Na(3D) state

The cross sections for electron-impact excitation of Na(3S) and Na(3P) atoms to the 3D state have been measured from threshold to 1000 eV, with ∼0.3 eV resolution. The 3P-state atoms are produced in the $m_l$=1, $m_s$=(1/2) level by optical excitation, and 3D→3P fluorescence is detected at 90° to the quantization axis. The resulting polarization anisotropies are considered, and included along with cascade effects in the high-energy normalizations to the Born approximation. The 3S→3D and 3P→3D excitation cross sections both rise very abruptly at threshold, and are indistinguishable from a step function with our energy resolution.