RADIATIVE LIFETIMES OF SEVERAL METASTABLE STATES OF DOUBLY AND TRIPLY IONIZED AR, KR, AND XE

The natural radiative lifetimes of the ns2np4 (1S0) metastable states of Ar2+, Kr2+, and Xe2+ 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 4s24p3 (2P1/2) metastable state of Kr3+ and also of the 5s25p3(2P1/2 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 x 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 logaxithm 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 1S0 metastable states of Ar2+, Kr2+, and Xe2+ 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 2P1/2 Metastable state of Kr3+ is 47 +/- 5 msec, while the lifetimes of the 2P1/2 and 2P3/2 metastable states of Xe3+ are 15.6 +/- 0.9 and 5.3 +/- 0.5 msec, respectively.