Radiative and relativistic effects in the decay of highly excited states in helium

A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 9 47 (1999)] measured a significant fluorescence yield of the He(2lnl') photo excited resonances, showing major qualitative differences from nonrelativis tic predictions. We present a further theoretical study of these states, an d perform R-matrix multichannel quantum defect theory calculations to extra ct fluorescence and ionization cross sections. These theoretical results ar e in excellent agreement with newer, higher-resolution measurements. Radiat ive and spin-orbit effects are quantified and shown to play an important ro le in the overall characterization of highly excited states.