Mean Life of the Metastable2P13State of the Two-Electron Oxygen Ion

The mean life of the metastable $2{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of the ${\mathrm{O}}^{6+}$ ion has been determined by measuring the decay length of the $1{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-2\mathrm{}{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{} (\lambda 21.8)$ radiation emerging from a 20-MeV beam of highly stripped oxygen ions. The result is ${\tau }^{-1\mathrm{}}=(6.6\mathrm{}\pm 0.5)\times {10}^8$ ${\sec }^{-1\mathrm{}}$ which compares favorably with our earlier measurement of (6 ± 1) × ${10}^8$ ${\sec }^{-1\mathrm{}}$. Mixing of singlet levels above $n=2\mathrm{}$, a feature of some recent calculations of this lifetime, is needed to bring about overlap of theoretical and experimental results. Additional information concerning excitation of one- and two- electron ions in such beams is presented.