Fourier Transform Infrared Spectrophotometer for Transmittance and Diffuse Reflectance Measurements

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Abstract
This paper describes a new Fourier transform infrared spectrophotometer with the capability to measure diffuse reflectance (DR) from 5000 to 500 cm−1 (2 to 20 µm) in addition to the normal transmittance measurements. The instrument has a true simultaneous double beam measurement mode and a high speed single beam mode. The system also takes advantage of many data manipulation and display features due to the built-in computer and 2.5 million word storage system. One of the objectives of this work was to produce a practical instrument which includes the DR capability; another was to introduce the qualitative and quantitative measurements of DR in the infrared to the analytical community. DR has been commonly available in the visible and near ir spectrum, but until this new instrument, has not been available in the ir. A brief survey of the background and history of DR and emittance measurements in the ir is given. The design details and operation of the instrument are generally examined. Brief examples are provided for a few transmittance, trace analysis, and microsampling applications, and a variety of DR results are shown. The addition of diffuse reflectance as a tool in the infrared opens new avenues for investigation and application in many fields.