Energies of some triplet levels in⁴He I

The authors have used saturated absorption spectroscopy and a sigmameter to obtain the absolute wavelengths of the 2p 3 P 0,1,2 -3d 3 D 1,2,3 transitions near 587.6 nm in 4 He I. The precision is about eight parts in 10 9 . By comparing with recent two-photon measurements of direct excitation from the 2s 3 S 1 level, they obtain values for the wavelengths of the 2s 3 S 1 -2p 3 P 0,1,2 transitions. Precision calculations for these transitions are compared with experiment. In particular, the authors discuss the QED and relativistic corrections. The relative energies of many triplet levels in He I are analysed.