Electron impact excitation of the 3 D-1 state of helium an electron-photoncoherence study at small scattering angles

Electron impact excitation of the 3 D-1 state of helium has been studied us ing the scattered electron-polarized photon correlation method. Results are presented at incident electron energies of 26.5, 29.6, 40.0, 45.0 and 60.0 eV for scattering angles up to 40 degrees. The data presented here complem ent the previous large angle data from this laboratory and taken together p rovide a complete mapping of the dimensionless parameters characterizing ex citation of the 3 D-1 state of helium over a wide range of both angle and e nergy. Strong variations in the parameters as a function of energy and angl e are discussed. Good agreement is observed between the experimental data a nd recent theoretical predictions.