Radiative Lifetimes of Excited Electronic States in Ionic Species of Nitrogen

The foil excitation technique, wherein a high-energy (2-MeV) beam of ions is passed through a thin (∼1000 Å) carbon foil, has been used to measure lifetimes of excited electronic states in nitrogen II through v. The lifetimes were obtained by measuring the decay of optical radiation as a function of distance from the foil. The excited states were considerably above the ground state of the particular ion, and as a consequence, nonlinear population by cascading was minimal. Because of the low speed of the optical system ($\frac{f}{8.8}$), only the most intense multiplets and members of multiplets were observed. The wavelength range in which transitions were observed was 2000 to 5000 Å. The lifetimes measured were between 0.4 and 10 nsec. In general, these lifetimes apply to all the members of the multiplet, since the levels of origin as well as the levels of termination are closely spaced with respect to the total-angular-momentum quantum number $J$. Where it is possible, these lifetimes are compared with available calculations. Some transitions are untabulated and were identified through the use of a computer program.