The predicted spectra of optEC_(s)(a)-modelled particles of radius 100 nm, presented as the wavelength times absorption coefficient per carbon atom, λα/N_C, in the 2 − 14   μm region (1 Mb  = 10^-18 cm²). Note how the spectra evolve from aliphatic-rich with prominent IR bands to aromatic-rich with no evident IR bands but a much stronger continuum. N.B. The bands with central positions long-ward of the vertical grey line (λ(ν₀) > 7.3   μm) are not yet well-determined by laboratory measurements.