Calculation of the electron impact coherence parameters for excitation of the 31D state of helium

First-order many-body theory (FOMBT) has been used to calculate the differential cross sections (DCS) and electron impact coherence parameters (EICP) associated with excitation of the 3 1 P, 3 1 D and 3 3 D states of helium for incident electron energies of 30, 40, 45 and 60 eV. No direct measurements of the DCS for excitation of the individual 3 1 P, 3 1 D and 3 3 D states have been reported but the sum of the theoretical DCS for excitation of these three states is in excellent agreement with that determined from recent electron energy loss data at 30 eV. The EICP predicted by FOMBT for excitation of the 3 1 D state are in good agreement with the recent measurements of Beijers et al (1986, 1987) but differ from FOMBT are qualitatively different from those obtained using the multichannel eikonal approximation. More accurate and extensive measurements will be needed to determine which of these two theories better describes the electron scattering process.