Abstract

The importance of two-electron transitions in the photoionization of atoms and molecules is well established and the photoionization of helium provides the simplest example of electron correlations in atomic physics. The simultaneous photoexcitation and photoionization of He occurs at photon energies >65.4 eV and has been studied by photoabsorption, photoelectron, and fluorescence spectroscopy. Each method is important in establishing absolute partial cross sections for ionizing neutral helium to He⁺ in the ns and np levels (n ⩾ 2) and for the study of the various autoionizing transitions that take place. The technique of fluorescence spectroscopy has proved to be a particularly simple and sensitive method to study the double excitation process.¹ Transitions into the 2p levels, either by direct photoionization or through autoionizing transitions, produce fluorescence radiation at 304 Å. Results obtained by this technique are discussed and compared with other methods.

© 1985 Optical Society of America