Effect of cascade transitions after electron-impact excitation of Zn by spin-polarized electrons.

We investigate the possible effect of cascade transitions from the $(4s5p)^3P_{0,1,2}$ states to the $(4s5s)^3S_1$ state of Zn. The polarization of the light emitted in the subsequent decay to the $(4s4p)^3P_{0,1,2}$ states has been the subject of recent controversy, with significant disagreement between the experimental data reported by Pravica {\it et al.}~[1] and by Clayburn and Gay~[2] in the cascade-free region below $\approx 7.6$~eV incident energy and relatively good agreement above. The cross sections for excitation of the $(4s5p)^3P_{0,1,2}$ states and the linear polarization of the cascade radiation seem too small to produce a significant alignment of the $(4s5s)^3S_1$ state, thereby raising additional questions regarding the origin of the relatively large linear polarizations measured above the cascade threshold. [1] L.~Pravica {\it et al.}, Phys. Rev. A {\bf 83} (2011) 040701). [2] N.~B.~Clayburn and T.~J.~Gay, Phys. Rev. Lett. {\bf 119} (2017) 093401.