Double photoionization of strontium

Resonant triple-differential cross-section (TDCS) measurements have been used to study the double photoionization process in strontium. Two sets of measurements were made at the photon energy of the 4p → 4d resonance. The coplanar geometry was used and the fixed analyser, positioned at -900 to the main axis of polarization of the photons, detected electrons with ∼65% of the available excess energy. The mutual angle between the two electrons had a range just short of 90 → 2700. The TDCS exhibit unexpected lobes at a mutual angle of 1800. Comparison with other measurements made with the same geometry but with different sharings of the available energy indicate that these TDCS all show the unexpected lobe. Some possible explanations for the lobe are considered.