Relative excitation functions for beam-foil populations in N II, N III, and N IV

Abstract

The authors have measured relative populations of terms in N II, N III, and N IV, excited after the passage of ${\mathrm{N}}^{+}$ ions through a carbon foil, as a function of the ion energy [$0.3<E(\mathrm{MeV})<1.9$]. These populations are obtained from the measurements of intensity of transitions emitted from these terms [$300<\ensuremath{\lambda}(\AA{})<1800$]. The variation of the ratio $R(E)$ of the relative population ${N}_{i}$ ($i$ is the term excited in the ion of charge $q$) to the equilibrium charge-state fraction $P(q)$ is studied as a function of the emergent beam energy. The grouping of the terms according to the number of electrons excited relative to the ground state shows that the $R(E)$ functions are generally different for the different groups of terms. Within a given group of terms (singly or doubly excited terms), the slopes of the $R(E)$ functions increase with the excitation energy of the term. These results are useful for classifying new lines observed in beam-foil spectroscopy.