The influence of collisional transfer of excitation energy in helium on the electron-impact excitation of the 4³D level

Absolute apparent cross sections for electron-impact excitation of helium to the 4³D level measured as a function of target-cross pressure (3*10^-5<p<3*10^-3 Torr) have been analysed by means of the 'F-cascade model'. proposed by St John and Fowler, (1961), in order to study the process of collisional transfer in helium. Special attention is paid to imprisonment of resonance radiation. It is found that scaling of the collisional transfer cross sections with a power of the principal quantum number n leads to results which are inconsistent with the experimental findings. By extrapolation of the apparent 4³D cross section to zero pressure we are able to estimate electron-impact excitation cross sections for the 4¹F level.