Radiative lifetime of metastable2S13Li+

The radiative lifetime of $1s2s{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ ${\mathrm{Li}}^{+}$ ions has been measured by a comparison of the count rate of spontaneous decay photons (210 Å) to a laser-induced fluorescence signal proportional to the total number of metastable ions. The ions were confined in a rf-quadrupole trap, and the fluorescence signal used was the intercombination transition $1s2p{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ to $1s^2{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ at 202 Å. The ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ state was populated from ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ by absorption of laser photons at 5485 Å. The result is ${\tau }_r=58.6\mathrm{}\pm 12.9$ sec (95% confidence level); theory predicts ${\tau }_r=49.1\mathrm{}$ sec.