Electric-field-induced singlet-triplet anticrossings in helium

Abstract

Anticrossing signals have been detected between n1D and n3D states of neutral He (n=5 to 7) using external electric field and internal singlet-triplet perturbations to couple the crossing states. Improved results for the n1D-n3D intervals are obtained: 34066.3(7.2), 20918.0(9.2) and 13632.8(5.3) MHz for n=5, 6, 7 respectively. This type of anticrossing also allows the study of the differential Stark effect, the anisotropic susceptibility chi A and the relativistic fine structure of the n3D states.