Wavelength coincidence of allowed and intercombination multiplets in N III and O IV - A density and/or temperature diagnostic

Two multiplets of N III with different intensity dependence on source conditions fall in the same wavelength interval near 1750 A, and the analogous multiplets in O IV also lie close together. It is suggested that the multiplet pair can be useful for diagnostic purposes. The calculated ratios are consistent with available observations. A preliminary inspection of solar flare spectra shows the presence of the higher-density-indicating allowed multiple in O IV.