Mid-IR Reflection Spectrometry

IR reflection spectrometry has found a number of applications. particularly for dealing with solid samples that are difficult to handle, such as polymer films and fibers, foods, rubbers, agriculture products, and many others. Mid-IR reflection spectra, although not identical to the corresponding absorption spectra, arc similar in general appearance and provide the same information as do their absorption counterparts. Reflectance spectra can be used (or both qualitatne and 

Diffuse-reflectance IR Fourier transform spectrometry (DRIFTS) is an effective way of directly obtaining IR spectra on powdered samples with a minimum of sample preparation.In addition to saving time in sample preparation, il permits conventional IR spectral data to be gathered on samples not appreciably altered from their original stale. The widespread use of diffuse-reflectance measurements had to await the general availability of F TIR instruments in the mid-107()s because tlie intensity of radiation reflected from powders is loo low to be measured at medium resolution and adequate signal-lo-noise ratios with dispersive instruments. 

Diffuse reflection is a complex process that occurs when a beam of radiation strikes the surface of a finely divided powder. W ilh this type of sample, specular reflection occurs at each plane surface. However, because there arc many of these surfaces and they are landomlv oriented, radiation is reflected in all direc- 

A number of models have been developed to describe in quantiialive terms the iiuensily of diffuse reflected radiation. The most widely used of these models was developed by Kubelka and Munk. Fuller and (iriffilhs in their discussion of this model show that the relative reflectance intensity for a pow-der t R ) is given by -  

To obtain a spectrum with a single-beam instrument, the signal for the sample is first stored. A reference signal with a good reflector, such as finely ground KBr or KCI, is then recorded in place of the sample. The ratio of these signals is then taken to give the reflectance. 

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A Mid-IR Absorption Spectrometry 455 17B Mid-IR Reflection Spectrometry 469 17C Photoacoustic IR Spectroscopy 472 17D Near-IR Spectroscopy 473 17E Far-IR Spectroscopy 476 17F IR Emission Spectroscopy 476 17G IR Microscopy 477... 

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