IR absorption spectra of the three soot samples after continuum subtraction. An offset has been added for visual convenience. The spectra were normalized altogether in order to match the intensity of the band at 1600 cm^-1. CO₂ spectral contamination at about 2400 cm^-1 for sample 2 and H₂O spectral contamination in the 1800−1400 cm^-1 range for sample 3 may be seen due to slight variations of the purge of the spectrometer. The vertical dotted line are centered on 3040, 1610, and 1250 cm^-1.