ABSTRACT
The infrared (IR) region of the electromagnetic spectrum is divided into three subregions, which are quite different from theoretical and application standpoints, and also require significantly different instrumentation. IR spectroscopy is undoubtedly one of the most versatile techniques available for the measurement of molecular species in the analytical laboratory. The basic concept of vibrational spectroscopy is first considered in terms of a simple diatomic molecule, to simplify the discussion to the vibration of a single, isolated bond. The concept of combining a microscope with a Raman spectrometer, to produce an instrument often known as a Raman microprobe, was developed simultaneously in France and in the United States in the mid-1970s. Virtually all of the discussion of IR instrumentation has centered around the fact that the technique is fundamentally a light absorption-based method of measurement. Like IR spectrometric instruments, Raman instruments fall into two main categories—dispersive instruments and interferometric instruments.
