Accurate calculations of double photoionization of noble gases

P. BOLOGNESI, A. KHEIFETS, S. OTRANTO, M. CORENO, V. FEYER, F. D. COLAVECCHIA, C. R. GARIBOTTI AND L. AVALDI

Ischia, Italia

Conferencia; 38th EGAS; 2006

The study of the photodouble ionization (PDI) of He via photoelectron-photoelectron or photelectronrecoil ioncoincidence experiments is the most suited approach to the study of the few-body Coulomb problem, a fundamental process in atomic physics. Indeed, the PDI of the He atom, with the simple 1Po symmetry of the electron pair and just a bare nucleus with no internal structure in the final state, is the prototypical example of the three-body Coulomb problem and the most suited process to study the electron-electron correlations. Since the first experiments in 1994 [1] the study of PDI in He via coincidence experiments has made noticeable progresses and a satisfactory experimental description and a good theoretical understanding have been reached [2]. In this contribution we show that the same experimental technique provides valuable information on the PDI process in the heavier rare gases. In particular the triple differential cross section (TDCS) of Ne(2s2) state at 20 eVabove its double ionization threshold has been measured in equal and unequal energy sharing conditions and perpendicular geometry and compared with the one of the He(1s2). The dynamical quantities which govern the photodouble ionization (PDI) process, i.e. the squared moduli of the gerade and ungerade complex amplitudes and the cosine of their relative phase, have been extracted from the experimental data. The results from the two targets have been compared between themselves as well as with the theoretical predictions of the SC3[3] and CCC calculations [4]. Despite the two targets share the same initial and final state symmetries some qualitative differences are observed in the TDCS. In equal energy sharing the differences can be explained as an initial state effect. The predictions of both the theoretical models are in reasonable agreement with the experiment when an accurate Ne 2s2 initial state wavefunction, which accounts for2s-2p intrashell correlation, is used. At variance in the case of the unequal energy sharing the use of the same wavefunction does not improve the agreement. This finding suggests that a complete description of the observed TDCS implies an extension of the used models to account properly for the correlation between the ejected electrons and the bound ones in the final state.This work represents a joint experimental and theoretical approach to the investigation  of PDI of atomic systems with more than two electrons. References [1]O. Schwarzkopf, B.Krssig,J. Elmiger and V.Schmidt, Phys. Rev.Lett. 70, 3008 (1993). [2]A. Huetz and L.Avaldi, J.Phys.B: At. Mol. Opt. Phys.38,S861 (2005). [3]S.Otranto and C.R. Garibotti, Eur. Phys. Jour.D21, 285(2002).    [4]A.Kheifets and I. Bray Phys. Rev. Lett. 81,4588(1998)