ENDOHEDRALLY CONFINED HELIUM ATOMS: MIRROR COLLAPSE, EFFECTS ON STRUCTURE AND DOUBLE PHOTOIONIZATION

D.M. MITNIK, J.M. RANDAZZO, F.D. COLAVECCHIA, AND G. GASANEO

Dublin

Conferencia; International Symposium on (e,2e), Double Photo-Ionization & Related Topics & 16th International Symposium on Polarization & Correlation in electronic & Atomic Collisions; 2011

Institute of Physics - Atomic and Molecular Interactions Group

One of the most fascinating features of the fullerene molecules [1] is that they arecapable of enclosing atoms in their hollow interior, forming endohedrally connedatoms [2]. It is expected that their atomic properties will be dramatically changedboth quantitatively and qualitatively, from those characteristic of the free atoms.Dolmatov et al. [3] studied the impact of the connement on various atomic features,such as the wavefunctions, energy levels, the lling of electronic shells, polarizability,photoabsorption and photoionization, etc. These processes have been thoroughlystudied for the endohedrally conned Hydrogen atom [4].In this work, the properties of a Helium atom conned inside an endohedral cavity,like a fullerene, are studied. Signicant simplications allowing us to uncover richvariety of eects which can occur in conned systems rather than to make detailedprecise predictions for a particular spectrum. Thus, we introduce a model in whichthe cavity is represented by a potential well and the strength of this potential isvaried in order to understand the collapse of dierent atomic wavefunctions intothe fullerene cage. We found, at rst glance, that the connement eects weredierent in Helium than in Hydrogen conned systems. In particular, we analyzedthe evolution of the energy spectra as a function of the depth of the conningpotential, and it was found to exhibit unusual level crossings. Only after developingan ecient computational method having a very high degree of precision { theGeneralized Sturmian basis method { we were able to show that the energy levelsdo not cross each other, but rather come close and repel each other yielding to anavoided crossing[5].We also studied[6] the double electronic emission by photon impact from groundstate of two-electron atoms conned in this model spherical fullerene. Triple dier-ential cross{sections show a strong dependence on the well depth and on the energyof the emitted electrons, due to the delocalization of the electrons in the initialstate. This simple system shows striking dierences with the electronic emissionfrom isolated atoms. The presence of the fullerene cage determines the structure ofthe cross{sections, breaking the initial state mirror collapse, and enhancing the roleof higher angular momentum waves of the ejected electrons in the process.References[1] Kroto H.W., Heath J.R., O'Brien S.C., Curl R.F., and Smalley R.E., Nature 318, 162 (1985).[2] Forro L. and Mihaly L., Rep. Prog. Phys. 64, 649 (2001).[3] Dolmatov V.K., Baltenkov A.S., Connerade J.P., and Manson S.T., Rad. Phys. and Chem. 70, 417(2004).[4] Connerade J.P., Dolmatov V.K., Lakshmi P.A., and Manson S.T., J. Phys. B 32, L239 (1999).[5] D.M. Mitnik J. Randazzo, and G. Gasaneo, Phys. Rev. A 78, 062501 (2008).[6] Colavecchia F.D., Gasaneo G., and Mitnik D.M., Jour. of At. Mol. and Opt. Phys., 2011, 817034(2011).