Low-energy electron impact coherence parameters for the S-1(0)-P-1(1) excitation 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 (...6s(2) S-1(0))-(...6s6p P-1(1)) inelastic process. Measurements of the natural parameters: gamma and P-lin(+) were made for excitation at impact energies of 5, 7.5, 9, 10 and 15 eV. Experimental data are compared with available theoretical results.