Fine structure and stark effect measurements on He+

Abstract

Anticrossing signals between magnetic sublevels from S and D and from S and F have been investigated in the n=4 state of He+. The anticrossing positions in the magnetic field are shifted by the electric field necessary to induce the signals. Extrapolation to zero electric been carried out, and the following fine structure separations have been derived from the crossing positions so obtained: present experiment theory (Erickson) 42S1/2 – 42D3/2 (20145.3 ± 7.8) MHz (20412.85 ± 1.36) MHz 42S1/2 – 42D5/2 (27455.4 ± 7.4) MHz (207458.60 ± 1.36) MHz 42S1/2 – 42F5/2 (27435.7 ± 13.8) MHz (27446.99 ± 1.36) MHz 42S1/2 – 42F7/2 (31098.2 ± 10.5) MHz (31104.78 ± 1.36) MHz From these measurements values of the Lamb shift separations for j>1/2 can be derived for the first time in this state: 42D5/2 – 42F5/2 (19.7 ± 20.0) MHz (1.61 ± 1.92) MHz 42P3/2 – 42D3/2 (34.4 ± 9.0) MHz (37.19 ± 1.36) MHz For the latter the present result for S¬1/2 – D3/2 is combined with the separation S¬1/2 – P3/2 of (20179.7 ± 1.2) MHz, measured by Jacobs et al. Experimental errors represent about 90% confidence limits, theory 6896. The shift of the anticrossing positions with the electric field allows investigation of the “Stark effect of the fine structure” at fields of fifty to a few hundred V/cm, a region inaccessible to spectroscopic investigations. Within the present accuracy of approximately 15-20% the quadratic Stark constants agree with calculations based on diagonalisation of the energy matrix in crossed magnetic and electric fields. In addition anticrossing signals have been observed in n=5, and “cascading anticrossings” 5S – 5G could be detected by their effect on the population of sublevels of n=4.