DIFFERENTIAL CROSS-SECTIONS AND THE ELECTRON-PHOTON COINCIDENCE PARAMETER-LAMBDA AND PARAMETER-VERTICAL-BAR-CHI-VERTICAL-BAR FOR THE ELECTRON-IMPACT EXCITATION 1(1)S-3(3)P IN HELIUM AT LOW ENERGIES

The 19-state and the 29-state R-matrix calculations have been employed to obtain the differential cross section and electron-photon coincide nce parameters lambda and \chi\ for the 1(1)S-3(3)P excitation of heli um at energies below the 5(1)P threshold. The results of the calculati on reported in this letter represent the first definitive calculation on these cross sections and lambda and \chi\ values expressed as funct ions of electron energies. The convergence between the R-matrix calcul ations is good. There is good agreement with recent experimental obser vations of Allan on the 3(3)P excitation functions. However, the agree ment with the experiments of Humphrey et al on the values of lambda an d \chi\ at 23.5 eV is far from satisfactory.