Measurement of the nitrogen(+) ((5)sulfide) state radiative lifetime
The radiative lifetime of metastable N{dollar}\sp{+}{dollar}(2s2p{dollar}\sp3{dollar} {dollar}\sp5{dollar}S{dollar}\sb2{dollar}) has been measured by directly monitoring the spontaneous emission from stored N{dollar}\sp{+}{dollar} in a radio-frequency ion trap. The electron excitation technique was used to create N{dollar}\sp{+}{dollar}({dollar}\sp5{dollar}S{dollar}\sb2{dollar}), and the spontaneous emission decay curve via spin-forbidden electric dipole transitions from 2s2p{dollar}\sp3{dollar} {dollar}\sp5{dollar}S{dollar}\sb2{dollar} to 2s{dollar}\sp2{dollar}2p{dollar}\sp2{dollar} {dollar}\sp3{dollar}P{dollar}\sb{1,2}{dollar} ground state at 2139.68 and 2143.55 A were observed. A measured value for the {dollar}\sp5{dollar}S{dollar}\sb2{dollar} radiative lifetime is {dollar}\tau\sb{\rm rad}{dollar} = 6.4 {dollar}\pm{dollar} 0.7 ms which is in good agreement with the theoretical result by Hibbert and Bates but longer than the measurement by Knight (4.2 {dollar}\pm{dollar} 0.6 ms). A careful study of non-radiative quenching and ion loss due to charge transfer of the metastable state was made. It was found that Knight's results were non-reproducible at a higher vacuum system with a meshed wall ion trap. This is perhaps due to unknown impurity gases in Knight's vacuum system. This measurement will clarify the discrepancy between Knight's measurement and theoretical calculations. An accurate value for the lifetime of the metastable N{dollar}\sp{+}{dollar}(2s2p{dollar}\sp3{dollar} {dollar}\sp5{dollar}S{dollar}\sb2{dollar}) ion is important in interpretation of the UV spectra of aurora.
Networked Digital Library of Theses and Dissertations