Ftir Theory

Theory A. Attenuated Total Reflection (ATR) There is a phenomenon called total reflection that a light beam will be totally reflected when it travels from a more refractive medium to less refractive one with incident angel greater than critical angel. Critical angel,

c  sin 1

2 1

where is η1 the refractive index of more refractive

medium and η2 is the refractive index of less refractive medium. In ATR, a highly refracting prism is used. Although the IR light beam is expected totally refracted, evanescent wave will get through to the shallow surface of the less refractive medium and absorbed by the sample that contact to the prism. B. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) Diffuse reflection and specular reflection are the components observed of reflection from solid surface. In DRIFT, light shines onto the powdered sample, specular component, where the light is reflected directly off, was blocked and diffuse reflectance, where the light penetrated, transmitted and reflected within the sample, was collected and analyzed.

Both of the methods can use in sample that is not pulverized or palletized easily which cause difficulty in analysis by typical methods.