PRECISION LIFETIME MEASUREMENTS OF N-II LEVELS WITH THE BEAM-FOIL LASER METHOD

Precision lifetime measurements using laser excitation of a fast ion beam preexcited in a carbon foil are reported for two levels in N ii. The cascade-free decays of the fluorescence intensities give lifetimes of 0.2490.004 and 0.2670.010 ns for the N ii 2p3d 1F°and 2p3s 1P°levels, respectively. The lifetime result for the 2p3d 1F°levelwhich is weakly repopulated by long-lived cascadesis in good agreement with beam-foil values and with the theoretical lifetime of McEachran and Cohen [J. Quant. Spectrosc. Radiat. Transfer 27, 119 (1982)]. The lifetime result for the 2p3s 1P°level which is strongly repopulated by cascades differs significantly from most of the previous experimental values but is in good agreement with the theoretical lifetimes of Luken and Sinanoglu [J. Chem. Phys. 64, 3141 (1976)], Beck and Nicolaides [Phys. Lett. 56A, 265 (1976)], McEachran and Cohen, and Fawcett [At. Data Nucl. Data Tables 37, 411 (1987)]. The f-value trend for the 2p2 1D 2p3s 1P°transition along the C i sequence is discussed. © 1990 The American Physical Society.