Complete Z-correlation diagrams for doubly excited 1Se states of the He isoelectronic series

We present in graphical form (Z-diagrams) an extension, to nuclear charges Z<2, of our previous study on doubly excited 1Se states of helium-like systems. The structure of the diagrams and closed-channel wavefunctions are discussed from the viewpoint of the quantum defect expression, which is coherent with an independent electron picture. Our analysis also contributes to a better understanding of the H- resonances. To apply to the complete Z-correlation diagram, the (N, nα) and (K, T) notation may be taken as equivalent, except in pseudocrossing regions where both labelling schemes break down. Energy ordering together with Z-diagrams provide the only general classification of doubly excited states. (author)