ELECTRON-IMPACT EXCITATION OF THE (2P2)3P DOUBLY EXCITED-STATE OF HELIUM

The excitation of the (2p2)3P doubly excited state of helium by electron impact has been studied in the energy range from threshold to 150 eV. This was done by observing the XUV radiation (32 nm) emitted in the decay of that state to the (1s2p)3P singly excited state. The shape of the measured excitation curve deviates appreciably from all existing theoretical results. In the threshold region clear evidence is found for the occurrence of negative-ion resonances.