Infrared Spectroscopy

The examination of infrared light interacting with a molecule is known as infrared spectroscopy. Absorption, emission, and reflection may all be measured to determine this. This approach is mostly used in organic and inorganic chemistry. Infrared waves have a longer wavelength and lower frequency than the visible light. Infrared Spectroscopy utilises the fact that molecules absorb frequencies respective to their characteristic structure. These absorptions occur at frequencies termed as resonant frequencies due to the fact that the absorbed radiation matches the vibrational frequency. 

The instrument used in the method of Infrared Spectroscopy is called the Spectrophotometer or an Infrared spectrometer. The Infrared Spectrometer produces an Infrared spectrum which can be depicted by the graph of absorption or transmission.

The characteristic units of frequency used in Infrared spectra are called wave numbers or reciprocal centimetres, with the symbol cm−1. The common units for the Infrared wavelength is given in micrometres which were previously called microns, symbol μm. The wavelength is always related to the wave number(frequency) in a reciprocal manner.

The Fourier Transform Infrared Spectroscopy

Fourier transform infrared spectroscopy is an analysis technique which enables us to read and record the infrared spectra employing the use of a Fourier transform infrared spectrometer commonly abbreviated as FTIR. The Fourier transform infrared spectroscopy uses a wide apparatus which includes a source, interferometer, sample compartment, detector, amplifier, and an A/D converter. The sample is illuminated by infrared light that passes via an interferometer (or vice versa). The distribution of infrared light passing through the interferometer is altered by a moving mirror inside the instrument. An “interferogram,” or directly recorded signal, depicts light output as a function of mirror position. 

The Fourier transform is a data-processing method that converts initial data into the desired outcome, which is the spectra of the given sample.

Fourier transform spectroscopy is a more accurate and yielding infrared spectroscopy than other common techniques because a FTIR spectrometer obtains high-resolution spectral data over a large spectral range at the same time. This gives it a big advantage over a commonly used dispersive spectrometer, which only measures intensity across a small range of wavelengths at a time.

What does the Infrared Spectroscopy principle depict?

The wavelength range for the section of the infrared spectrum which is the most effective for organic chemical analysis is 2,500 to 16,000 nm, with a frequency range of 1.9*1013 to 1.2*1014 Hz. Photon energy levels in this region of the infrared spectrum (from 1 to 15 kcal/mole) are too low to excite electrons, but they can cause vibrational excitation in covalently bound atoms and groups.

The Infrared spectroscopy principle proved that light atoms having stronger bond strength vibrate at a higher frequency than the normal bonded atoms. The vibrations of atoms may be measured using infrared spectroscopy, and by this method, functional groups in the sample are determined. Chemists use infrared spectrometers to produce compound absorption spectra that are a unique reflection of their chemical structure.

Infrared spectroscopy is also alternately defined as the measurement of detected infrared intensity against wavelength (or frequency) of light, which is the most basic report acquired in spectroscopic processes.

Applications of Infrared Spectroscopy

• Determining the reaction kinetics – The progress of a chemical reaction can be assessed by periodically withdrawing a little quantity of the reaction mixture. The rate of disappearance of a characteristic absorption band of the reactant group and/or the rate of emergence of a characteristic absorption band of the product group as a result of product creation are monitored.
• Recognising similar compounds- Infrared spectroscopy provides valuable information about determining if one sample of an organic compound is identical to another. This is due to the presence of a vast number of absorption bands in the IR spectra of organic molecules, and the likelihood that any two substances would yield identical spectra is essentially nil. So, if two compounds have similar infrared spectra, they must be samples of the same material.

• Determining impurities in chemical compounds – The Infrared Spectra of the to-be-determined test sample is compared to that of the standard chemical. If any additional peaks are seen in the IR spectrum, they are caused by impurity defects in the molecule.      

Conclusion

Infrared spectroscopy (IR spectroscopy) is a type of spectroscopy that explores and utilises light in the infrared spectrum to illuminate a chemical sample and extract data in the form of its wavenumber, wavelength, and other properties. which has a longer wavelength and lower frequency than visible light. Fourier transform infrared spectroscopy (FTIR) converts raw data (interferogram) into an observable spectrum using the Fourier transform mathematical technique. The infrared spectrum of transmission or absorption of the chemical sample is obtained using the FTIR technique. In a chemical sample, FTIR detects the existence of organic and inorganic components.