Theoretically simulated IR spectra of two molecular structures with C₁₅H₁₆ formula at T = 500 K. The blue and red profiles represent MAON (1,3-diphenylpropane; Fig. 7a) and PAH with aliphatic side groups (Fig. 7b). A quantum chemical model of B3LYP/PC1 is applied to calculate the vibrational normal modes. The solid black lines indicate the positions of the UIE features seen in Hb 12. The positions of UIE features marked with green, blue, red, and black colours indicate the bands reproduced by both models, by the MAON model and the PAH+aliphatics model, and by none of the models, respectively.