Fluorescence of helium doubly excited states

The fluorescence decay of helium doubly excited states converging to the He+(n=2) threshold has been measured after their excitation by synchrotron radiation. Photons emitted at 0degrees and 90degrees with respect to the polarization axis of the incident radiation have been measured and show a new aspect of the role of relativistic effects (spin-orbit) in the transition from the LS to the jK coupling scheme. The detection of metastable singly excited helium atoms, formed as by-products of the radiative decay, is the most sensitive channel for the observation of triplet doubly excited states. The lifetimes of members of the 2pnd series have been measured and indicate a deviation from what could be expected from the commonly accepted (K,T) A quantization of doubly excited states.