Collective motion in closed shells

Current interest in the stability of closed shells stems from several different areas of research. The subject of giant resonances [5] will be described later in the present book. It involves collective motion of all the electrons in a closed shell or subshell, and their cooperative response is therefore of interest [6]. 

In high harmonic generation experiments [9], atoms are subjected to superintense laser fields, in which the motions of the driven electrons 

In quite another area of physics, the discovery of magic numbers in alkali and other metallic clusters [7] has provided a fresh example of the significance of electronic shell closure. These much larger shells have been shown to oscillate collectively, and the resulting oscillations are of great significance as an example of a many-body resonance. They are discussed at some length in chapter 12. 

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