No abstract

The energy spectra of ground-state, ionized and excited multielectron atoms and ions of the 3d and 4d periods of the periodic table centred in impenetrable spherical confinement are detailed using Hartree-Fock configuration average calculations. It is shown explicitly for the first time that, owing to modifications in 3d and 4d orbital collapse, the filling of shells for the confined transition sequences becomes more regular than for free atoms with increasing confinement pressure, that s-d competition disappears, and that, for d-excited states, the crossings between inner-shell excited states and the double-ionization thresholds are altered. In general, the periodic table for confined (compressed) atoms can differ from that for free atoms. The importance of these findings for different branches of basic and applied physics and chemistry is indicated.

The properties of hydrogen confined endohedrally at the geometrical centre of a spherical, attractive short-range potential shell are explored. The evolution of the energy spectrum, as a function of the depth of the shell, is found to exhibit unusual level crossings and degeneracies resulting in avoided crossings and a new phenomenon of 'mirror collapse' where the localized states switch places. In addition, a new level ordering, principally by the number of nodes in the radial wavefunction, develops. The results apply generally to endohedrally confined atoms. Further, they suggest a new tool for controlling the properties of atoms.

Three different types of resonances arise in the photoionization spectra of atoms endohedrally confined within a fullerene cage: atomic resonances, confinement resonances and molecular resonances. In each case, a different mechanism is involved, and different theoretical models are necessary for their study. In this work, we exploit the flexibility of the spherical modelpotential method to explore the properties of confinement resonances. Both repulsive and attractive shells are considered. It is demonstrated that the nature of confinement resonances (CRs) emerging in each case is not the same. For attractive shells it is found that CRs result from interference between three waves: the incident wave, and the waves reflected at each of the inner and outer cavity boundaries. We find significant sensitivity of near-threshold confinement resonances to the size and thickness of the shell, we demonstrate modulations and 'beats' in the intensities of the resonances and we study them, both as a function of the parameters of the confining shell, and as a function of photoelectron energy. In the case of repulsive shells, the resonances can result from three-wave interference, as above, or can be due to quasi-discrete states appearing as a result of confinement.

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 β 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.