Excitation of the 4F States of Helium*

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Recent studies of the population processes of the 4F state in helium by observation of the infrared radiation from this state have given direct experimental evidence for the 41P to 4F excitation-transfer process. The behavior of the apparent cross sections of the 41P and 4F states with pressure is used to evaluate the cross section for the excitation transfer and the cross section for electronic excitation to the 4F state. Analysis of the data indicates a cross section of 1.5 × 10−14 cm2 for the 41P to 4F transfer and 1.6 × 10−19 cm2 at 100 eV for the electron excitation plus cascade of the 4F state. Apparent cross sections of the 4F state are presented at high and low pressures from onset to 450 eV. At high pressure the apparent cross section is similar to that of the 41P state. As the pressure is lowered, the shape of the excitation function approaches that of a 1D state.