The IR spectroscopy is an absorbed spectroscopic method generally used in the field of analytical chemistry and materials characterization, as well as in physical chemistry for the study of chemical bonds what is FTIR spectroscopy.
When an infrared photon is absorbed by a molecule, it passes from its fundamental vibrational state to an excited vibrational state. In a particular infrared expanse on the absciss we discover a scale of commonness expressed in wave quantity, or quantity of tides per cm, and in the ordinate the percentage of transmittance.
If a material is transparent to infrared radiation, its spectrum will appear as a line parallel to the abscissa axis. If a material is not completely transparent there will be absorptions and therefore transitions between vibrational energy levels. In this additional trial, the recorded range will be distinguished by a sequel of peaks of inconsistent elevation for each growth.
Schematically, a classic IR spectrophotometer essentially consists of a source whose light beam is directed towards the sample and the reference, the latter usually consisting of the liquid in which the sample is dissolved. This is followed by the monochromator whose function is to select a specific wavelength and a chopper (optical system in the shape of a semi-disc which in double-beam instruments is also placed after the source to split the light beam) which alternately addresses the detector the radiation coming from the sample and the reference respectively. The detector is the final component that generates a signal as a function of the concentration of analyte present.
The commonly used IR sources are of the incandescent type and are represented by Nernst filaments consisting of sintered oxides, globars formed by silicon carbide rods and which require external cooling.
From the infrared spectrum it is possible to obtain useful information for the recognition of an unknown molecule. In this regard, in order to associate a link to a given wave number, specific tables reported in the bibliography or electronic libraries included in the instrumentation software are used.
That the attenuated total reflectance (ATR, English attenuated total reflectance) is a sampling technique of infrared spectroscopywhich exploits the reflection of the ray passing through the sample. In this technique, the sample is placed in close contact with an optical element called an internal reflection element (or ATR crystal) consisting of a crystal with a high refractive index. The IR ray emitted by the source, before reaching the sample, first passes through this element: when the angle of incidence is more than the critical angle, the happening known as total reflection occurring. This reflected flash, arriving on the surface of the sample which constitutes the interface, can penetrate up to a thickness of 2 µm of the less refracting material. In this way it forms an evanescent wave, which following the absorption of radiation by the sample will result in an attenuated radius; in this way, the ATR spectrum can be recorded.