Infrared Spectrometry

Meilyn E. Rivera Peña

As one of my mayor interest is chemistry, I have learned about multiples instruments and methods to measure. One of these methods is the infrared spectroscopy (IR) that has a wavelength range from 2,500 to 16,000 nm and a frequency range from 1.9*1013 to 1.2*1014 Hz. The IR spectroscopy has different techniques, mostly based on absorption spectroscopy. It can be used to identify and study chemicals, as with all spectroscopic techniques. During the World War II, it was used for the synthesis of synthetic rubber (used in the control of concentration and purity of the butadiene used in the synthesis of the polimer). The IR spectrum is divided in three regions: near, med and far IR, named for their relation to the visible spectrum. The higher energy (near IR) is approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength), the mid IR is approximately 4000–400 cm−1 (2.5–25 μm), and the far IR is approximately 400–10 cm−1 (25–1000 μm). Those three different regions are used to determine the harmonic vibrations, the rotational-vibrational structure and the rotational spectroscopy, respectively. The IR spectroscopy is about the rotation and vibration of the molecules, which means that the molecular movements of rotation and vibration have discrete energy levels. The frequency or wavelength of each mode of absorption is a function of the relative mass atoms, the force constant of the bonds and the geometry of the vibration. This makes possible assigning frequencies bending elongation characteristics and specific functional groups, and that while the vibrational frequency for a given link in a complex molecule are completely independent of the other links located near the range of variation is small. That this should be noted that only one peak is observed in the IR spectrum, extension or flexion, is accompanied by a change in the dipole moment. Likewise, the more polar a bond stranger the peak corresponds to the frequency of vibration. The most common application of IR spectroscopy in organic chemistry is qualitative and resides in the qualitative identification of certain functional groups in a molecule for characteristic bands that can be observed in certain regions of the spectrum. It is used in research and the industry like a simple and confident practice to realize measures, quality control and dynamic measures. Some machines of this spectrum show automatically which the substance measured by a lot of reference spectrum is saved. By measuring at a specific frequency over time, it can measure changes in the nature of amount of a particular link. This is particularly useful for measuring the degree of polymerization in the manufacture of polymers. Modern machines research infrared measurements can be taken throughout the entire range of interest at a frequency of x32 per second. This can be accomplished while performing simultaneous measurements using other techniques. This makes the observation of chemical reactions and processes more quickly and accurately. The IR spectrum is related to the physics class because it is a combination of studies and theories by Hamilton, Born-Oppenheimer and other chemist and physicians. 

References:

http://www.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm

http://ocw.um.es/ciencias/experimentacion-en-quimica-organica-avanzada/material-de-clase-1/eqoa-tema-1.pdf

http://en.wikipedia.org/wiki/Infrared_spectroscopy