Scattering parameters for the electron impact excitation of the 5 1D2 to 6 1P1 transition in Ba

Studies of electron impact excitation of excited state atoms are few in number and pose a new challenge for theory. The authors report on measurements of differential scattering parameters for the electron impact excitation of the (...6s6p 1P1) state in barium from the metastable, isotropically populated, (...6s5d 1D2) level at 20 eV impact energy. Five independent parameters are required to characterize this excitation (by unpolarized electrons); the differential cross section and four electron impact coherence parameters. The determination of these parameters was made by carrying out superelastic scattering studies involving electron impact de-excitation of the laser-excited (...6s6p 1P1) state. The authors will discuss the novel laser excitation geometry and measurement scheme employed