Transferred orbital angular momentum in the low-energy electron impact excitation of the 1S0-1P1 transition in barium

Superelastic electron scattering involving the collisional de-excitation of laser-excited Ba-138(... 6s6p P-1(1)) atoms to the (... 6s(2) S-1(0)) ground state has been used to measure electron impact coherence parameters for the related (... 6s2 S-1(0)) to (... 6s6p P-1(1)) inelastic process. Measurements of the orbital angular momentum transfer parameter, L-perp(+), were made for excitation at impact energies of 7, 8.5, 11 and 16 eV. Experimental data are compared with available theoretical results.