Photo double-ionization of helium: A new approach combining R matrix and semiclassical techniques in an hyperspherical framework

We introduce a new method for computing photo double ionization (PDI) cross sections for two electron atoms. It is formulated in terms of the hypersph erical radius R and relies upon a combination of R matrix techniques in the inner region R less than or equal to R-0 with a semi classical approximati on for the R motion in the outer region. We present a first application of this method to the PDI of He within a model of reduced dimensionality where r1=r2. it demonstrates the validity of our numerical scheme and provides a first quantitative estimate of the energy domain of validity of the Wannie r mechanism.