DIFFERENTIAL CROSS-SECTIONS OF HELIUM FOR 1(1)S-2(3)S, 2(3)P BY ELECTRON-IMPACT AT 100 AND 200 EV

The R-matrix method is used to calculate differential cross sections for the transitions 1(1)S to 2(3)S 2(3)P in helium by electron impact at incident energies 100 and 200 eV. An 11-state and a polarized pseudo-state calculation are performed. Present results are compared with new experimental results of Sakai et al for the transition 1(1)S - 2(3)S and with theoretical results of Fon et al, who included five states in an R-matrix calculation. It is seen that the present theoretical calculations for 1(1)S - 2(3)S at 200 eV do not fully reproduce the large cross sections found at low angles in the experiments, although the present results are in good agreement with those at large angles.