Excitation and polarization of the 3(3)D state of helium by electron impact

Electron impact excitation of the 3(3)D state of helium has been studied ex perimentally and theoretically using the convergent close coupling (CCC) an d R-matrix with pseudo-states (RMPS) methods. Experimental and theoretical CCC emission cross sections and polarizations of the 3(3)D --> 2(3)P line a re reported. Theoretical cross sections for direct excitation of the 3(3)D state and polarizations of corresponding emitted radiation are also reporte d using both CCC and RMPS methods. Particular attention has been given to m aking realistic estimates of the large cascade contributions to both the cr oss sections and the polarization fraction of the 3(3)D --> 2(3)P radiation , using the CCC approach. The self-consistency of the experimental and theo retical polarization data gives confidence in their quality. On the other h and differences remain between experimental and theoretical emission cross sections at higher energies.