ELECTRON-IMPACT COHERENCE PARAMETERS FOR THE (...6S5D(1)D(2)) TO (...6S6P(1)P(1)) EXCITATION IN BA-138 DETERMINED BY SUPERELASTIC SCATTERING MEASUREMENTS

Superelastic electron scattering involving the de-excitation of laser- excited Ba-138 (...6s6p(1)P(1)) to the lower-lying (...6s5d(1)D(2)) me tastable level has been investigated. These measurements have been use d to extract the electron impact coherence parameters which describe e xcitation out of an isotropic (...6s5d(1)D(2)) level to the higher-lyi ng (...6s6p(1)P(1)) state. Studies have been carried out for an electr on impact energy of 20 eV and a range of scattering angles up to 45 de grees. This investigation represents a significant extension of cohere nce parameter measurements to inelastic transitions between excited at omic levels.