Radiative lifetimes of metastable states ofHg+andHg2+

The natural radiative lifetimes of the 5${\mathit{d}}^9$6${\mathit{s}}^2$ ${(}^2$ ${\mathit{D}}_{5/2}$ and ${}_{}{}^2{}_{}{}^{}$ ${\mathit{D}}_{3/2}$) metastable states of ${\mathrm{Hg}}^{+}$ as well as of the 5${\mathit{d}}^9$6s${(}^3$ ${\mathit{D}}_2$) metastable state of ${\mathrm{Hg}}^{2+}$ have been measured by counting for equal time intervals either the 282-, 198-, or 217-nm photons emitted when the respective metastable ions decay to the ground state. The metastable Hg ions are produced inside a cylindrical electrostatic ion trap by electron bombardment of background Hg vapor maintained at pressures ranging from 4 to 50×${10}^{\mathrm{-}8}$ Torr. The trap consists 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 140 V. Following electron impact of the Hg vapor, some of the photons emitted by the decaying metastable ion population are focused onto a narrow-bandwidth interference filter. The photons transmitted by the filter are detected by a photomultiplier tube as a function of time and generate a decay curve. However, the signal detected with the interference filter used to monitor the ${}_{}{}^2{}_{}{}^{}$ ${\mathit{D}}_{3/2}$ metastable-state population consists of two exponentially decaying components, indicating the presence of another metastable state decaying through the emission of a photon within the bandpass of the filter. The second component is assumed to arise from a cascade originating with the 5${\mathit{d}}^9$6s6p (J=9/2) metastable state of ${\mathrm{Hg}}^{+}$. Therefore, as dictated by the composition of the photon decay curve, the pressure-dependent decay rates of the metastable states are obtained from a least-squares fit of either a single- or double-component exponential decay to the natural logarithm of the decay curve.