Energies of some triplet levels in4He I

Abstract
The authors have used saturated absorption spectroscopy and a sigmameter to obtain the absolute wavelengths of the 2p 3P0,1,2-3d 3D1,2,3 transitions near 587.6 nm in 4He I. The precision is about eight parts in 109. By comparing with recent two-photon measurements of direct excitation from the 2s 3S1 level, they obtain values for the wavelengths of the 2s 3S1-2p 3P0,1,2 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.