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

The natural radiative lifetimes of the ns²{np}⁴(¹{S}₀$) metastable states of ${Ar}²⁺$, ${Kr}²⁺$, and ${Xe}²⁺$ 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${s}²$4${p}³(²{P}1/2$) metastable state of ${Kr}³⁺$ and also of the 5${s}²$5${p}³(²{P}1/2$ and $²P3/2) metastable states of Xe³⁺. The decay rate of each state was determined by counting for equal time intervals the uv photons emitted as the metastable ion population decayed to a lower level of the ground-state configuration. A population of ions was produced inside a cylindrical electrostatic ion trap by electron bombardment of the appropriate parent gas maintained at pressures ranging from 4 to 80×{}10^-8 Torr. The trap consisted of a 5.0-cm-diam, 7.5-cm-long cylinder with end caps plus a concentric 0.003-cm-diam central cylinder maintained at a negative potential of 150 V. Following electron impact of the parent gas, some of the photons emitted by the decaying metastable ion population were focused onto a narrow-bandwidth interference filter.Photons transmitted by the filter were detected by a photomultiplier tube as a function of time and generated a decay curve. As dictated by the composition of the photon decay curve, the pressure-dependent decay rate of each metastable state was obtained from a least-squares fit of either a single- or double-component exponential decay to the natural logarithm of its decay curve. The mean decay rate was extrapolated to zero pressure of the parent gas using a straight-line least-squares fit, and the inverse of the zero-pressure intercept yields the natural radiative lifetime of the relevant metastable state. Our measurements for the ¹{S}₀$ metastable states of ${Ar}²⁺$, ${Kr}²⁺$, and ${Xe}²⁺$ yield 133±{}24, 14.8±{}0.8, and 4.6±{}0.3 msec for the natural radiative lifetime of the respective metastable state. Our result for the lifetime of the ²{P}1/2$ metastable state of ${Kr}³⁺is 47±5 msec, while the lifetimes of the²P1/2 and ²{P}3/2$ metastable states of ${Xe}³⁺$ are 15.6±{}0.9 and 5.3±{}0.5 msec, respectively.