MEASURED LIFETIMES OF SELECTED METASTABLE LEVELS OF ARQ-TRAP( IONS (Q=2, 3, 9, AND 10) STORED IN AN ELECTROSTATIC ION)

Metastable multiply charged argon ions produced in, and extracted from , an electron cyclotron resonance ion source were captured from the be am into an electrostatic (Kingdon) ion trap by rapidly pulsing the pot ential of the central wire relative to the cylinder. The ions were sel ected on a charge-to-mass ratio basis before capture. Photons emitted in magnetic-dipole and electric-quadrupole transitions from levels wit h lifetimes exceeding 5 ms were selected by wavelength and recorded vs ion storage time in the trap. Also, ions were counted after ejection following a preselected storage time in the trap, using a microchannel plate detector. These signals were studied as a function of the press ure of typical residual gases. Extrapolation to zero pressure enabled the extraction of the lifetimes tau of metastable levels from four dif ferent configurations of the type ns2np(k) with n = 2 or 3 and k = 3, 4, or 5. Our experimental results are tau(Ar2+, 3s(2)3p4 S-1(0)) = 159 .7 +/- 9.7-38.4 ms, tau(Ar3+, 3s(2)3p3 P-2(3/2)) = 243 +/- 73-79 ms, t au(Ar9+, 2s(2)2p5 P-2(1/2)) = 8.53 +/- 0.24-0.17 ms, and tau(Ar10+, 2s (2)2p4 P-3(1)) = 14.8 +/- 1.1-0.48 ms. Both statistical errors and a p ossible error associated with a systematic correction are given for ea ch measurement. These results are compared with the predictions of the oretical calculations, many previously untested. The basis of the meas urement technique is discussed in some detail. The technique is expect ed to be applicable to ions in a large range of charge states from a v ariety of low-energy ion sources, and to levels with transitions from the near-infrared to the deep-ultraviolet or soft-x-ray range.