  Experimental results on partial photo-ionisation cross sections of helium are
analysed in the light of recent advances in the semiclassical theory of
two-electron atoms. Byun et al (arXiv:physics/0701086) predict that the total
photo-ionisation cross section below the double-ionisation threshold can,
semiclassically, be described in terms of contributions associated with
classical orbits starting and ending in the triple collision. The necessary
modifications of the semiclassical theory for partial cross sections is
developed here. It is argued that partial cross sections are also dominated by
the triple collision dynamics. The expected semiclassical contributions can be
identified in the Fourier transformation of the experimental data. This clearly
demonstrates for the first time the validity of the basic assumptions made in
Byun et al. Our findings explain furthermore in a natural way the self-similar
structures observed in cross section signals for different channel numbers.
