The lifetime of the bound excited level in Ni$^-$

The intrinsic lifetime of the upper level in the bound-bound 3d$^9$4s$^2$ $^2$D$_{3/2}$ $rightarrow$ 3d$^9$4s$^2$ $^2$D$_{5/2}$ radiative transition in Ni$^-$ was measured to be 15.1 $pm$ 0.4 s. The experiment was performed at cryogenic temperatures in one of the ion-beam storage rings of the DESIREE (Double ElectroStatic Ion Ring Experiment) facility at Stockholm University. The storage lifetime of the Ni$^-$ ion-beam was measured to be close to five minutes at a ring temperature of 13 K.