Photo-double ionization of rare gases by circularly polarized photons

F. D. COLAVECCHIA, S. OTRANTO AND C. R. GARIBOTTI

Freiburg, Alemania

Conferencia; XXV International Conference on Photonic, Electronic and Atomic collisions (ICPEAC); 2007

The Photo-Double ionization of He results in a clear three body Coulomb final state, and becomes the archetype reaction to evaluate the existing models for the two electron continuum [1]. However, analytical descriptions of the two electron continuum give appropriate descriptions of the angular distributions and proved a cheap way to gain insight into the main physics of the process at the expense of sacrificing other important aspects, as the gauge agreement or the absolute magnitude of the cross sections. Recently, PDI of noble gases other than He showed to be an important challenge even for numerical methods due to the multielectronic character of the targets [2]. For the He case, both linearly and circularly polarized photons were considered theoretically as well as experimentally and the dependence of the fully differential cross sections on the photon helicity was established [3,4]. For Ne and Ar targets, only linearly polarized photons have been measured [2,5]. The angular distributions of electrons emitted from noble gases show richness of features larger than the He case. The multielectronic character of the target sets and important challenge to the evaluation of PDI and, even numerical methods require additional assumptions for description of data [2]. In this work,we consider the PDI of Ne gases by means of circularly polarized photons. In the evaluation of the PDI amplitudes, the two electron continuum is represented by the well-known C3 model and two different initial states employed: an uncorrelated product of two optimized Clementi-Roetti type wave functions, and a correlated CI expansion. Amplitudes are evaluated using different orientation of the photon polarization, obtaining those corresponding to positive and negative photon helicity and circular dichroism (CD). In Fig. (1) we display our theoretical results for the CD of PDI in Ne(2s2) target, for sake of comparison we include results and dat for He(1s2). We note that by definition, the CD is symmetric around q2=p, in any case. The CD for Ne(2s2) and HE(1s2) exhibit similar features. However, we will show that the double photoionization of p states increases the number of lobes in the electron angular distribution and the complexity of the CD. In this case the definite helicity cross sections attain zero values and the CD show deep extreme values.   Fig. 1 Circular dichroism parameter for He and Ne   This work has been supported by PIP 5595 of CONICET, PICT 04/20548 of ANPCyT and PGI 24/F038 of UNS (Argentina).   References   [1] J. S. Briggs and V. Schmidt, J. Phys. B 33, R1 (2000) [2] P. Bolognesi et al., J. Phys. B 31, 1899 (2006) [3] V. Mergel et al, Phys. Rev. Lett. 80, 5031 (1998) [4] J. Berakdar, J. Phys. B 32, L27 (1999) [5]  B. Krassig et al, J. Phys. B 29, 4255 (1996)