Fine structure of the1s4fconfiguration of helium

By use of an rf electric resonance technique, the fine structure of the 1s4f multiplet of He i and its splitting in a static electric field have been investigated. Our results for the fine-structure intervals ${\nu }_{1\mathrm{J}}$ between the ${}_{}{}^1{}_{}{}^{}\mathrm{F}_3^{}{}_{}{}^{}$ level and the ${}_{}{}^3{}_{}{}^{}\mathrm{F}_{\mathrm{J}}^{}{}_{}{}^{}$ levels are ${\nu }_{12}$=232.8(2.0) MHz, ${\nu }_{14}$=490.8(2.0) MHz, and ${\nu }_{13}$=704.3(1.0) MHz. Furthermore, a singlet-triplet mixing ratio Ω=0.757(3) and the exchange interaction 2K=158(3) MHz have been derived from the measurements.