ELECTRON-IMPACT EXCITATION OF HELIUM AT 26.5 EV

We present convergent close-coupling (CCC) calculations and measuremen ts of 26.5 eV electron-impact excitation of the ground state of helium . The present measurements extend the experimental information at this energy to include 3(3)D excitation. The CCC theory is compared with a ll of the available 2(1)P,3(1)P,3(1)D,3(3)D measurements, the agreemen t with which is very satisfactory and comparable to that at higher imp act energies. [S1050-2947(97)06110-6].