Dipole channels of two-electron atoms

The Z dependence of dipole excitation channels in two-electron atoms is investigated for levels N<or=6. An SO(4) group theoretical approach is used to classify these spectra; at low Z the channels are assigned quantum numbers from a Stark representation SO(4)=SU(2)*SU(2), while at high Z there is an alternate set of quantum numbers from the symmetry-breaking chain SO(4) contains/implies SO(3). Rules are described for correlating the two sets of quantum numbers, and appear to be related to the number of nodes in the wavefunctions with respect to the interelectronic angle theta 12. Due to the existence of a second constant of the motion, the dipole channel spectrum is found to contain numerous crossings. Some crossings are described near Z=1 which could lead to a breakdown of the dipole approximation, and interference in e-+H channels originating in the short-range part of the interaction potential.

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