Abstract
The 33P1-33P2interval in4He is measured by the step-wise excitation level-crossing technique at 658.76+or-0.13 MHz, in fair agreement with the previous measurement by Wieder and Lamb (1957). The n3D fine-structure intervals are calculated by extending the theory of Van den Eynde et al. (1971), and fairly good overall agreement is obtained with recent experimental intervals, notably those of Astner et al. (1976). The singlet-triplet mixing coefficients of Van den Eynde et al. are recalculated using experimental singlet-triplet splittings, giving results in excellent agreement with the experimental values of Derouard et al. (1976).