Carbon as Reference for Normalizing Infrared Photoacoustic Spectra

Photoacoustic spectra of solids¹ are usually “source compensated,” i. e., normalized for differences in source emission at different wavelengths, and such compensation is done by comparing the photoacoustic spectrum of a sample to the emission spectrum of the source measured directly with, say, a photocell,² power meter,³ or photodiode,⁴ or to the photoacoustic spectrum of “carbon” recorded under the same conditions as that of the sample. A variety of carbons has been used for this purpose, including carbon black on silica,⁵ soot from a gas torch,⁶ and acatylene-sooted bakelite,⁷ such a reference substance being assumed to be a flat black absorber. That assumption appears to be valid, as indicated by the close