Radiative lifetimes of theS01metastable states ofKr2+andXe2+

The radiative lifetimes of the ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$ metastable states of ${\mathrm{Kr}}^{2+}$ and ${\mathrm{Xe}}^{2+}$ have been measured to be 13.1±0.6 and 4.5±0.3 msec, respectively. The ions were created by electron bombardment on the neutral parent gas and contained in a cylindrical radio-frequency ion trap. A single-photon-counting photomultiplier tube was used to observe directly the subsequent spontaneous emission. The transitions observed were, for ${\mathrm{Kr}}^{2+}$, the M1 (magnetic dipole) transition at 350.5 nm from ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$ to ${}_{}{}^3{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ in the 4$p^4$ ground configuration, and, for ${\mathrm{Xe}}^{2+}$, the M1 transition at 380.1 nm from ${}_{}{}^1{}_{}{}^{}\mathrm{S}_0^{}{}_{}{}^{}$ to ${}_{}{}^3{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ in the 5$p^4$ ground configuration. The experimental results are in fair agreement with theoretical predictions.