INELASTIC ELECTRON-SCATTERING BY LASER-EXCITED BA-138( ... 6S6P P-1(1)) ATOMS

We present experimental and theoretical results of an investigation in to low-energy electron scattering from Ba-138 atoms coherently prepare d in the (...6s6p)P-l(1) state by laser excitation. We measured the di fferential cross section from the coherently prepared (...6s6p)P-1(1) state (referred to as partial differential cross section) for excitati ons of the (...5d(2))P-3(2), (...6p5d)F-1(3), (...6s6d)D-1(2), (...6s7 p)P-1(1), (...6s8s)S-3(1), and (...6s8d)D-1(2) levels at E-o = 20 eV a nd 36.7 eV incident electron energies and compared them with theoretic al results obtained from unitarized distorted wave approximation calcu lations. In some cases (e.g, the excitation of D-1(2) and P-1(1) level s) there is reasonable or good agreement between theory and experiment , in other cases (e.g, the excitation of the P-3(2) and S-3, levels) t here are order of magnitude (or more) differences.