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A.G. Calamai (ASU)
The 2s2p3 5S2 metastable level of N+ has received significant attention from both the atomic physics and planetary science communities over the past twenty years. The N+ ion is a driving component in the ionosphere of Titan, where N2 collisions with magnetospheric electrons have sufficient energy for the production of the N+ metastable levels. This report addresses the current status of the 2s2p3 5S2 radiative lifetime. Agreement appeared to exist between theory and experiment until the later part of 1998, when the lifetime was again measured at the TSR storage ring in Heidelberg, Germany. The high precision reported with the TSR measurement cast significant uncertainty on N+( 5S2) lifetime. In response, we used a relatively new technique to correct for ion losses, the radiative decay curves associated with the fluorescence of a metastable N+ population confined to a cylindrical radio-frequency (rf) ion trap. The apparatus includes time-of-flight mass resolution to accurately monitor the time evolution of the N+ population. The ion-correction technique uses the ion-storage efficiency data, obtained from the TOF mass spectra, to adjust the observed radiative decay curves on a point-by-point basis. Moreover, with the adjusted radiative decay curves, if the collisional de-excitation rates of the metastable levels are similar to the ground-state ion population, the corrected radiative decay curves yield the radiative lifetime of the metastable level without pressure extrapolation. The current result, 5.6±0.1 ms, for the lifetime of the 2s2p3 5S2 metastable level of N+ will be presented and compared to past theoretical and experimental results.
This work was partially supported through Grant No. CC5274 from the Research Corporation.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.