An angular correlation function for double photoionization in atoms

We consider the successive emission of two electrons following the absorption of a photon by an atom. An expression for the angular correlation between the emitted electrons is derived in terms of the angle between their directions of propagation, following the generalized approach of Biedenharn and Rose (Rev. Mod. Phys. 25 (1953) 729). Our theory treats double photoionization as a two-step process and does not refer to perturbation theory. The dynamics of the process are embodied in the reduced matrix elements. It is clear that angular correlation is closely related to the coupling of the angular momenta. A sample computation is made for double photoionization in argon leading to the 3p(-2) D-1(e) final ionic state. (C) 2001 Elsevier Science B.V. All rights reserved.