Abstract
Photoacoustic spectroscopy has been used to study TlI powders used in thin film coating applications. The spectra obtained show differences between what was regarded as good coating material from that which was unacceptable. Good material displayed a sharp absorption edge at 440 nm and no tailing off at the transparent side of the edge. The ratio of signals on the opaque side of the edge divided by that on the transparent side was largest for good material. Much of the poorer material contained absorbed I2 within the material. It was found that material exposed to the atmosphere would evolve I2 gas. Differenence spectra between freshly mounted TlI and evolved materials closely resemble absorption spectra of I2 gas.
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