Anticrossing studies of HE+,n=4

Abstract

Higher order, S-D and S-F, anticrossing signals induced by a static electric field were investigated to measure the fine structure splittings between magnetic sublevels from S and D and from S and F in the n=4 levelne+ . The excited helium ions were produced by electron bombardment parallel to the magnetic field. The signal centres which are shifted by the electric field were extrapolated to the zero field. Effects of experimental parameters like current, excitation voltage and in particular the pressure were investigated. The following fine structure values were derived from the crossing positions of the signals. Intervals Present Experiment Theory (MH,) Eric (MHZ) (1977) 4F7/2"4Sl/2 31100.7 + 2.4 31103.84 + 0.04 4F5/2_4Sl/2 27438.1 + 3.1 27446.06 + 0.04 4D5/2-4Sl/2 27455.8 + 4.6 27459.02 + 0.04 4D3/2-4Sl/2 20143.2 + 3.9 20143.27 + 0.04 The electric field necessary to induce the signals causes a shift of the crossing centres and so allowed the measurement of the low field Stark effect of this hydrogenic system. The quadratic Stark effect dominates in most cases and the quadratic Stark constants obtained with about 2% accuracy are in agreement with the theoretical calculation based on the diagonalisation of the energy matrix in combined II electric and magnetic fields. A theoretical study was made to calculate the signal shape on the basis of the full fine structure system to derive theoretical values of the crossing entres and Stark constant.