Influence of electronic correlation on the electron impact excitation of the doubly excited3Pgand1,3Dustates of helium. I. The Born-Oppenheimer approximation

Integral and differential cross sections for the parity-unfavoured excitations of the 3 P g and 1,3 D u states of helium have been calculated using the Born-Oppenheimer approximation for the scattering amplitude and a variety of estimates for the ground-state wavefunction of the helium atom. These cross sections are found to be much more sensitive to the choice of target wavefunction than single-excitation cross sections which previously have been investigated. Thus, the integral cross section for excitation of the 3 P g state is only half as large when calculated with a 35-term CI helium ground-state wavefunction as with a Hartree-Fock function.