Absorption spectra of hexachlorobenzene adsorbed on SiO2 powders

Photoacoustic spectra of hexachlorobenzene adsorbed on SiO2 powders of different particle sizes were investigated. A comparison of the measured PA spectra with the calculated optical absorption lengths μβ led to the conclusion that only absorption bands for which μβ is much larger than the particle size, i.e. in the case of carrier transparency, appear in the PA spectrum. This indicates that the particle diameter determines the thickness of the sample. Compared to their solution spectra the PA spectra of HCB on the silica carriers do not show a red shift of the various absorption bands as was claimed in the literature.