Many-Electron Effects in the Absorption and Emission of VUV Radiation by Atoms and Ions

We demonstrate that the absorption and emission of VUV radiation by atoms and ions is determined to a large extent by many-electron or correlation effects. Some of these were discovered a number of years ago, while the others have been observed only recently. We illustrate the discussion of correlation effects, considering the case of photon absorption. Then demonstrate that almost the same effects which show up in VUV absorption are also very important in emission. Any deviations from the predictions of the simple hydrogen-like picture in photoabsorption cross-sections are due to the many-electron nature of the atom and in this sense are many-electron effects.