The Infrared Examination of Carbons with Beam Deflection Spectroscopy

Abstract

The use of infrared (IR) photothermal beam deflection spectroscopy (PBDS) for the examination of carbons is described. The PBD signal generated with carbons consists of two components. One is electronic in origin, the semiconductivity of the carbon giving rise to an intense LR continuum absorption. It is this IR continuum that makes it so difficult and frequently impossible to examine carbons by conven- tional IR spectroscopic techniques. Superimposed of the intense IR continuum is the weaker second component, due to the vibrational modes of the carbon structures. Observing the intensity of the IR con- tinuum can lead to useful information concerning the degree of poly- aromatization of the carbon. The observation of the vibrational modes is particularly valuable because information about the nature and reactivity of the functional groups on the carbon surface can be ob- tained. Conventional IR spectroscopic techniques have not been very useful for the study of carbons. With the exception of coals and chars produced at relatively low tempera- tures, both of which are partially 1R-transmitting, most carbons absorb so strongly that the conventional trans- mission/absorption techniques usually fail. Similarly, IR internal reflection spectroscopy has had but little success because the technique is so cumbersome and irreprc lu- cible as to be unmanageable. Also, so far, diffuse reflec- tion and photoacoustic techniques have not been applied to detailed studies of carbons (l). However, a step in what appears to be the right direction has been taken via pho- tothermal beam deflection spectroscopy (PBDS). Some results are described.