Spatially and temporally averaged synthetic spectrum, compared with observations from RASOLBA (Staath & Lemaire 1995) and HRTS-9 (Morrill & Korendyke 2008). The transmission function for the IRIS 279.60 nm slit-jaw filter is also shown (in arbitrary units). Also noted are the locations of the photospheric lines used in Section 4.3 and the quasi-continuum groups used in Section 4.4. The inset shows the location of the k ₁, k ₂, and k ₃ spectral features.