Calculated spectra (black) compared to experimental optical emission spectra (red) of shock-induced coronene. Self-absorption was taken into account in the simulations. Adjusted values for ϵ, [C₂] and T_gas: (a) 0.06, 2.3×10¹⁵ molecule cm⁻³, 4000 K; (b) 0.137, 1.8×10¹⁶ molecule cm⁻³, 4000 K; (c) 0.18, 2×10¹⁶ molecule cm⁻³, 4000 K and (d) 0.08, 5×10¹⁵ molecule cm⁻³, 3500 K. Contamination by iron (Fe I) (527 nm) was also identified.