An Optical Accessory for Obtaining the Infrared Spectra of Very Thin Films

In 1959, Francis and Ellison (1) described a procedure for obtaining the infrared spectra of monomolecular and thicker layers of fatty acids and fatty acid salts on various metallic substrates by a multireflection technique. To accommodate the accessory optics and the associated increase in length of optical path between the source and photometer section of a Perkin-Elmer Model 21, the source optics were modified. Such a modification is undesirable if the instrument is to be used for transmission or specular reflectance measurements. Therefore, an optical design was derived which would permit installation and removal of the accessory without requiring undue changes in the basic instrument.