V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia Endohedrally confined atoms in Fullerenes: He (and the time capsule) Dario Mitnik 1 , Juan Randazzo 2 , Flavio Colavecchia 2 , y Gustavo Gasaneo 3 1 Instituto <strong>de</strong> Astronomía y <strong>Física</strong> <strong>de</strong>l Espacio y Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> <strong>de</strong> Buenos Aires, Argentina 2 Centro Atómico Bariloche, Río Negro, Argentina 3 Depto. <strong>de</strong> <strong>Física</strong>, <strong>Universidad</strong> Nacional <strong>de</strong>l Sur, Bahía Blanca, Argentina email address corresponding author: dmitnik@df.uba.ar One of the most fascinating features of the fullerene molecules [1] is that they are capable of enclosing atoms in their hollow interior, forming endohedrally confined atoms. Experimental efforts have ma<strong>de</strong> it possible to trap atoms insi<strong>de</strong> a fullerene in different ways. The particular mechanisms responsible for the insertion of the atom, vary from a “brute force" implantation, to a “window" mechanism, in which high temperatures and pressures can break one of the Carbon- Carbon bonds in the cage. Small molecules and atoms can pass through this temporary hole, forming a stable endohedrally confined compound. The properties of a Helium atom confined insi<strong>de</strong> an endohedral cavity, like a fullerene, are studied. The fullerene cavity is mo<strong>de</strong>led by a potential well and the strength of this potential is varied in or<strong>de</strong>r to un<strong>de</strong>rstand the collapse of different atomic wavefunctions into the fullerene cage. Three theoretical calculation methods have been <strong>de</strong>veloped: a relaxation method, a Sturmian basis method, and a variational method. The first two methods are nonperturbative. The three methods allow inclusion of full correlations among the two electrons. Results showing mirror collapse effects are presented for an S-wave mo<strong>de</strong>l, in which all the angular quantum numbers are set to zero. In this work [2] we showed how the confinement potential strength affects in different amounts the atomic levels of the confined atom. Figure 1. First three wavefunctions, 1s2 1S, 1sy1 1S, and 1sy1 3S for different potential <strong>de</strong>pths, around the first avoi<strong>de</strong>d crossing at U0=1,185 a.u.. Around the regions <strong>de</strong>noted as crossings, it seems that the variation in the potential produces <strong>de</strong>generacies in energy, indicating that the levels can cross each to the other. A <strong>de</strong>tailed analysis that requires a very high <strong>de</strong>gree of precision shows that the energy levels do not cross each other, but rather come close and repel each other yielding to an avoi<strong>de</strong>d crossing. We analyzed the behaviour of the avoi<strong>de</strong>d crossing levels by using different information entropies, providing an efficient tool to estimate in a physically transparent manner the 26 Valparaíso, Chile
V Encuentro Sud Americano <strong>de</strong> Colisiones Inelásticas en la Materia atomic transitions caused by a slowly varying perturbation. References [1] Kroto H.W. et al., Nature 318, 162 (1985). [2] Mitnik, et al., Phys. Rev. A 78, 062501 (2008). 27 Valparaíso, Chile