K-shell X-Ray Emission from Lithium-like Nitrogen N V

We present laboratory measurements of n = 3 → n = 1 N V X-ray emission lines situated near 26 Å. The lines are excited by electron-impact collisions and are shown to reach a combined intensity of about a fifth of the combined strong N V 1s2s2p ² P _1/2,3/2 → 1s ²2s ² S _1/2 resonance lines, commonly labeled q and r, at 29.4 Å. In addition, we present new experimental data for the wavelength of the blended q and r lines at 29.4 Å, as well as for that of the blended inner-shell-excited N V lines u and v at 30.0 Å. All of these collisional N V lines need to be included in astrophysical emission models in order to properly account for flux from N V in the soft X-ray region. The measured wavelengths provide benchmarks for testing atomic structure calculations and excellent agreement is found with our calculations using the many-body perturbation theory method. We provide a complete listing of the N V energy levels with valence electrons in the n = 2, 3, and 4 shells calculated with this approach. The experimental and theoretical data, thus, provide accurate rest-frame wavelengths needed for velocity determinations based on high-resolution absorption features in spectra of warm absorbers in active galactic nuclei and other astrophysical objects.