Hyperfine-Induced 1s2s ${}^1{S}_0$-1s2p ${}^3{P}_0$ Transition and Fine-Structure Measurement in Heliumlike Nitrogen

We have observed the $1s2s{}^1{S}_0-1s2p{}^3{P}_0$ transition in ${}^{14}{\mathrm{N}}^{5+}$ using Doppler-tuned fast-beam laser spectroscopy. This transition, absolutely forbidden for atoms with zero nuclear spin, occurs due to mixing of states of different $J$ by the hyperfine interaction. By measuring the difference between the $2{}^1{S}_0-2{}^3{P}_{1,F}$ and $2{}^1{S}_0-2{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ transition energies, we have obtained a value for the $1s2p{}^3{P}_1-{}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$ fine-structure splitting in ${\mathrm{N}}^{5+}$. Our result will test quantum-electrodynamic corrections to recent high precision calculations [Z.-C. Yan and G. W. F. Drake, Phys. Rev. Lett. 74, 4791 (1995)].