Radiative lifetimes of several metastable states of doubly and triply ionized Ar, Kr, and Xe

The natural radiative lifetimes of the ${\mathit{ns}}^2$ ${\mathit{np}}^4$ ${(}^1$ ${\mathit{S}}_0$) metastable states of ${\mathrm{Ar}}^{2+}$, ${\mathrm{Kr}}^{2+}$, and ${\mathrm{Xe}}^{2+}$ with n=3, 4, or 5, respectively, have been measured using an ion-trapping technique. In addition, we have measured the natural radiative lifetimes of the 4${\mathit{s}}^2$4${\mathit{p}}^3$ ${(}^2$ ${\mathit{P}}_{1/2}$) metastable state of ${\mathrm{Kr}}^{3+}$ and also of the 5${\mathit{s}}^2$5${\mathit{p}}^3$ ${(}^2$ ${\mathit{P}}_{1/2}$ and ${}_{}{}^2{}_{}{}^{}$ ${\mathit{P}}_{3/2}$) metastable states of ${\mathrm{Xe}}^{3+}$. The decay rate of each state was determined by counting for equal time intervals the uv photons emitted as the metastable ion population decayed to a lower level of the ground-state configuration. A population of ions was produced inside a cylindrical electrostatic ion trap by electron bombardment of the appropriate parent gas maintained at pressures ranging from 4 to 80×${10}^{\mathrm{-}8}$ Torr. The trap consisted of a 5.0-cm-diam, 7.5-cm-long cylinder with end caps plus a concentric 0.003-cm-diam central cylinder maintained at a negative potential of 150 V. Following electron impact of the parent gas, some of the photons emitted by the decaying metastable ion population were focused onto a narrow-bandwidth interference filter.