A unique situation for an endohedral metallofullerene

This letter demonstrates for the first time that an endohedral environment, such as the bucky-ball C 60 , can produce a significant redistribution of oscillator strengths in endohedrally trapped atoms, making the dominant transitions no longer superior but inferior, and also making electron correlations in such atoms act in an opposite way to free atoms. This is exemplified by calculations of the oscillator strengths and photoionization cross sections of the Ca atom trapped inside C 60 . Also, while photoionization cross sections can undergo dramatic changes on confinement, the photoelectron angular asymmetry parameter n can, in contrast to natural expectation, remain largely unchanged. The random-phase approximation with exchange was employed. We believe these are the first calculations of electron correlations for confined atomic species.