Fine structure measurement in He⁺, n=4. I. Intervals S-F

Electric field induced anticrossing signals are used to measure the fine structure splittings S-F of n=4 in ( 4 He) + . The crossing positions have been extrapolated to zero electric field. The present results are (27435.7+or-13.8) MHz for the interval 4 2 S 1/2 - 4 2 F 5/2 and (31098.8+or-10.5) MHz for the interval 4 2 S 1 2/-4 2 F 7/2 in agreement with the theoretical values of (27466.99+or-1.36) MHz and (31104.78+or-1.36) MHz respectively. The interval 4 2 F 5/2 -4 2 F 7/2 is derived to (3663.1+or-24.3) MHz compared with (3657.78+or-0.01) MHz from the theory.