Physical Review A
The Hylleraas-Scherr-Knight variation-perturbation method is applied to the calculation of oscillator strengths for the dominant transitions from the metastable 2p3p P3 and 2p3d D1,3 states of helium and the heliumlike ions. The results explain the absence of the 1s2pP3-2p3pP3 transition of He i from recent beam-foil excitation spectra. © 1972 The American Physical Society.
Drake, Gordon W. F.. (1972). Radiative transition rates from the 2p3p P3 and 2p3d D1,3 states of the helium isoelectronic sequence. Physical Review A, 5 (2), 614-619.