ELECTRON-IMPACT EXCITATION OF THE 1(1)S-]3(1)P AND 1(1)S-]4(1)P TRANSITIONS IN HELIUM

The method of electron-photon coincidence is used to ''resolve'' the e lectron-impact excitation of the n P-1 levels (n=3 and 4) from nearby levels. Experimentally determined ratios of the differential cross sec tions for the electron-impact excitation of 1 S-1-->2 P-1, to 1 S-1--> 3 P-1, and 4 P-1 transitions are presented at 30-, 40-, and 80-eV inci dent electron energies. Differential cross sections for the 1 S-1-->3 P-1 and 1 S-1-->4 P-1 transitions are derived by normalizing these rat ios to available experimental differential cross sections for the 1 S- 1-->2 P-1 transition. The ratios and differential cross sections are c ompared to available theoretical and semiempirical data.