ELECTRON-IMPACT EXCITATION OF THE N(3,1)S AND N(3,1)P (N=2, 3 AND 4) STATES OF HELIUM AT LOW ENERGIES

The 19-stare and 29-state R-matrix calculations are employed to obtain the differential cross sections and electron-photon coincidence param eters for the 1(1)S-n(3,1)S and 1(1)S-n(3,1)P (n = 2, 3 and 4) excitat ion of helium at energies ranging from the ionization threshold to 31. 2 eV. The scattering angle ranges from 0 degrees to 180 degrees. The r esults are compared with the experiments and the latest calculation of Pray and co-workers to estimate the contributions of the effects of i onization continuum. Attempts are also made to show that the angular d istribution of scattered electrons of the same incident velocity that have excited the n(3,1)S (or n(3,1)p) levels of helium for n = 2, 3 an d 4 are almost identical when fitted together at one angle.