The imaginary part of the dielectric function, ϵ₂, for the optEC_(s) model (lines without data points) compared to laboratory and other model data (lines with data points). The diamond (purple and violet lines) and graphite data (black) are shown for comparison. The vertical dashed lines mark the band centres of the π − π^∗, C₆ and σ − σ^∗ bands at 4.0, 6.5 and 13 eV, respectively.