Infrared (IR) microscopy, also known as vibrational spectroscopy is a method of analysis that takes advantage of the vibrational transitions of a molecule. It is among the most widely employed spectroscopic techniques utilized by organic and inorganic chemical scientists due to its effectiveness in determining the structure of molecules and in identifying them. The technique or method of using infrared spectroscopy involves an instrument known as an infrared-spectrometer (or a spectrophotometer) to create the infrared spectrum.
Principle of Infrared (IR) Spectroscopy
Infrared Spectroscopy is the analysis of infrared light that interacts with molecules. The infrared spectrum that is most suitable to study organic compounds has an infrared wavelength of between 2,500 and 16,000 nm and a frequency range of 1.9*1013 to 1.2*1014 the frequency of which is Hz. The photon energies that are that are associated with this portion of infrared (from 1 to 15 kcal/mole) aren’t enough to trigger electrons, however, they could trigger vibrational excitation of the covalently bonded atoms and groups.
It is well-known that, in addition to the easy rotation of groups around one bond, molecules undergo an array of vibrational motions that are characteristic of their atoms. In turn, all organic compounds absorb infrared radiation , which corresponds in energy to the vibrations. Infrared spectrometers are similar in concept to other spectrometers allow chemists to get absorption spectra for compounds which reflect an exclusive representation of the molecular structures.
The most fundamental measurement made by Infrared spectroscopy is the infrared spectrum. This is a graph of the measured infrared intensities versus the frequency (or frequency) of light. IR Spectroscopy examines the vibratory patterns of atoms and on this , it’s possible to identify which functional groups. The more strong bonds and lighter atoms oscillate at a higher stretch frequency (wavenumber).
Instrumentation of Infrared (IR) Spectroscopy
The principal components of IR the spectrometer are:
- Radiation source
- Sample cells and sampling of substances
IR radiation sources
IR instruments require the use of a source of energy that emits IR radiation that must be constant and intense enough to be detected and extend to what is needed in the wavelength.
The various types of IR radiations are listed below.
- Nernst glower
- Incandescent lamp
- Mercury arc
- Tungsten lamp
- Glober source
- Nichrome wire
Sample cells and sampling of substances
IR spectrum has been employed to characterize gas, liquid or solid samples.
- Solid – A variety of methods are employed for the preparation of solid samples, including the pressed pellet method solid run-in-solution mull technique, solid films and so on.
- Liquid – Liquid samples can be stored in the liquid sample cell that is composed of alkali halides. Solvents that are aqueous cannot be used since they dissolve alkali halids. Only organic solvents, such as chloroform can be utilized.
- Gas– It is similar to the sampling of liquids.
There are many kinds of monochromators: prisms, gratings, and filters. Prisms are constructed of Potassium bromide Sodium chloride, or Caesium Iodide. Filters are comprised of Lithium Fluoride, and Diffraction gratings comprise alkali Halides.
Detectors can be used to measure the strength of the infrared radiation. They include thermocouples, Bolometers, thermisters Golay cells, as well as pyroelectric detectors are employed.
Recorders are devices used to capture all aspects of the IR spectrum.
Graph of the IR spectrum
Below is a small example of the typical Infrared Absorption Frequency.
So, IR spectroscopy involves the gathering of absorption data and the analysis of that information as an IR spectrum.
Applications of Infrared (IR) Spectroscopy
It has been of major importance to scientists in diverse fields like:
- Protein characterization
- Nanoscale analysis of semiconductors as well as
- Space exploration.
- Analyzing gaseous, liquid or solid samples
- Identification of compounds
- Quantitative analysis
- Information on the functional groups of molecules as well as the structure of molecules could be derived by IR spectrum
- To learn about interactions between molecules