Reflectance Spectroscopy

Reflectance spectroscopy is the investigation of the spectral composi tion of surface-reflected radiation with respect to its angularly dependent intensity and the composition of the incident primary radiation. Two limiting cases are important: The first concerns regular (specular) reflection from a smooth surface, and the second diffuse reflection from an ideal matte surface. All possible variations are found in practice between these two extremes. For the two extreme cases, two fundamentally different methods of reflectance spectroscopy are employed: The first of these consists in evaluating the optical constants n (refractive index) and x (absorption index) from the measured regular reflection by means of the Fresnel equations as a function of the wave A. This rather old and very troublesome procedure, which is length incapable of very accurate results, has recently been modified by Fahren fort by replacing the air-sample phase boundary by the phase boundary between a dielectric of higher refractive index (n ) and the sample (n ). 1 2 If the sample absorbs no radiation and the angle of incidence exceeds a certain definite value, total reflection occurs. On close optical contact between the two phases, a small amount of energy is transferred into the less dense phase because of diffraction phenomena at the edges of the incident beam. The energy flux in the two directions through the phase boundary caused by this is equal, however, so that 'total reflection takes place.

The main subject division of this book include the theory of Diffuse reflectance spectroscopy; measurement and standardization of diffuse reflectance; instrumentation; application to color measurement and physical, inorganic, and organic chemistry; and applications in chromatographic analysis.While the use of reflectance spectroscopy dates from the 1920s, it has only been in the last decade that its analytical potential has been developed. Interestingly, much of the early research involved industrial uses where measurement of color was required. The development and acceptance of thin-layer chromatography has opened up new areas of analysis for the application of this technique.It is not the purpose of this book to delve deeply into the theoretical aspects of reflectance spectroscopy, as this book has already been done in several previous books. Insofar as it is possible, this book is an up-to-date guide to instruments and techniques intended primarily for the chemical analyst, though it is hoped that it may contain information of interest to other scientists. The potential for the application of this technique is great and the authors feel confident that the coming decade will see many interesting developments in this type of spectroscopy study, particularly in the field of analysis.

This volume contains all of the papers presented at the American Chemical Society Symposium on Reflectance Spectroscopy. The Symposium was presented under the sponsorship of the Division of Analytical Chemistry, and was held on September 11 and 12,1967, at the 154th National Meeting of the American Chemical Society, Chicago, Illinois. The papers presented herein represent a renaissance of interest in reflectance spectroscopy. The techni~ue of reflec tance spectroscopy is not, of course, a new techni~ue, however, it has only been applied to problems of a chemical interest in the last decade or so. The instrumentation for this techni~ue in the ultraviolet, visible, and near infrared regions of the spectrum has been available for many years. New and exciting research is being carried out at the present time to extend these techni~ues to the infrared and far infrared regions as well. It is a pleasure for the Editor to express his gratitude to Drs. John K. Taylor and E. C. Dunlop of the Division of Analytical Chemistry, ACS, for their cooperation in making the Symposium a reality. The assistance of Miss Julie Norris of the University of Houston for her typing and manuscript organi zation skill is greatly appreciated. And lastly, but certainly not the least, the Editor would like to acknowledge the coopera tion of all of the contributors to this volume. Certainly without their cooperation, this Symposium would not have been a success.

The main subject division of this book include the theory of Diffuse reflectance spectroscopy; measurement and standardization of diffuse reflectance; instrumentation; application to color measurement and physical, inorganic, and organic chemistry; and applications in chromatographic analysis.While the use of reflectance spectroscopy dates from the 1920s, it has only been in the last decade that its analytical potential has been developed. Interestingly, much of the early research involved industrial uses where measurement of color was required. The development and acceptance of thin-layer chromatography has opened up new areas of analysis for the application of this technique.It is not the purpose of this book to delve deeply into the theoretical aspects of reflectance spectroscopy, as this book has already been done in several previous books. Insofar as it is possible, this book is an up-to-date guide to instruments and techniques intended primarily for the chemical analyst, though it is hoped that it may contain information of interest to other scientists. The potential for the application of this technique is great and the authors feel confident that the coming decade will see many interesting developments in this type of spectroscopy study, particularly in the field of analysis.

An essential reference for researchers and students of planetary remote sensing on the interaction of electromagnetic radiation with planetary surfaces.

Presents coverage of internal reflection spectroscopy (IRS) and its applications to polymer, semiconductor, biological, electrochemical and membrane research. It describes the theory and procedures and identifies the spectral regions, from materials characterization to process monitoring.