Excitation and polarization of the 33D state of helium by electron impact

Electron impact excitation of the 33D state of helium has been studied experimentally and theoretically using the convergent close coupling (CCC) and R-matrix with pseudo-states (RMPS) methods. Experimental and theoretical CCC emission cross sections and polarizations of the 33D→23P line are reported. Theoretical cross sections for direct excitation of the 33D state and polarizations of corresponding emitted radiation are also reported using both CCC and RMPS methods. Particular attention has been given to making realistic estimates of the large cascade contributions to both the cross sections and the polarization fraction of the 33D→23P radiation, using the CCC approach. The self-consistency of the experimental and theoretical polarization data gives confidence in their quality. On the other hand differences remain between experimental and theoretical emission cross sections at higher energies. (author)