Orientation dependence of inelastic scattering from the laser-excited (…6s6p¹P₁) state of barium

We have investigated inelastic electron scattering from the laser-excited (…6s6p¹P₁) state of barium at 20 eV incident electron energy and scattering angles of 5.5°, 9°, 13°, and 16°. By using circularly polarized laser light and measuring the circular polarization dependence of inelastic energy loss features associated with various excitations, we have determined the transferred orbital angular momentum parameter. L_perp⁺ for the time-inverse related deexcitations X⃗(…6s6p¹P₁), where X=(…6s7p¹P₁), (…6s6d¹D₂), (…6s7s¹S₀), (…5d²³P₂) and the unresolved states (…5d²¹D₂,…6p5d¹D₂). Our structure calculations show some of these states to be essentially pure, two-electron states with relatively strong singlet-triplet mixing. Scattering calculations were carried out in the convergent close-coupling formalism and, in general, good agreement with experimental data is shown. A detailed analysis of the S⃗P and D⃗P deexcitations in comparison to previously reported results for S⃗P and D⃗P excitations [Y. Li and P. W. Zetner, Phys. Rev. A 49, 950 (1994); P. V. Johnson, B. Eves, P. W. Zetner, D. Fursa, and I. Bray, Phys. Rev. A 59, 439 (1999)] shows a selection rule of Δm=+1(-1) to hold for excitation (deexcitation) in small-angle scattering.