Who invented infrared spectroscopy

The most important pioneer of IR spectroscopy was William W. In he published the result of a large study of compounds whose spectra he had recorded from nm to 16, nm.

These absorptions are the result of interactions with the fundamental vibrations of the chemical bonds associated with the atoms of the groups. We can think of chemical bonds as weak springs holding together two or more atoms, these springs will vibrate naturally and when energy is added to the system then they will vibrate more energetically.

However, atoms in molecules are constrained by quantum mechanics so that only a few specific energy levels are allowed. If we have only two atoms then the only vibration will be seen as a stretching. When three or more atoms are involved then bonds can also bend, giving rise to a whole series of different vibrations.

Stretch vibrations require more energy than bending vibrations but there will also be variation in the energy requirements of the bending vibrations. Different chemical bonds like O—H, C—H and N—H vary in strength and hence the amount of energy required for the bond vibration to move from one level to the next.

This variation in energy will be seen in a spectrum as a series of absorptions at different wavelengths. By looking at the spectrum we can deduce what vibrations are occurring and hence work out the structure of the molecule or groups of atoms present. While the study of mid-IR spectroscopy continued to grow, especially after World War II, interest in the NIR extended to quantitative measurements of water, a few simple organic compounds and a very few studies of specific proteins.

No one considered it useful for characterising samples and it was considered too complex for use in quantitative analysis. If chemical bonds behaved exactly like weak springs then quantum mechanics would restrict their vibration to just two states and there would be very few absorptions in the NIR region. Absorptions in the NIR region — nm are generated from fundamental vibrations by two processes; overtones and combinations.

Overtones can be thought of as harmonics. So every fundamental will produce a series of absorptions at approximately integer multiples of the frequency frequency is the reciprocal of wavelength. Combinations are rather more complex. NIR absorptions are at a higher state of excitement so they require more energy than a fundamental absorption.

Combinations arise from the sharing of NIR energy between two or more fundamental absorptions. While the number of possible overtones from a group of fundamental absorptions in a molecule are limited to a few, a very large number of combinations will be observed. The effect of all these absorptions combine to make many NIR spectra to look rather uninteresting and to consist of only a few rather broad peaks.

Figure 2 is an NIR spectrum of chloroform, CHCl 3 , the molecule contains only one hydrogen atom but all the absorption in its spectrum are caused by this single atom. It is an important generalisation that NIR spectroscopy is dominated by hydrogen. Figure 3 is a spectrum of methanol, CH 3 OH, which contains four hydrogen atoms but three are equivalent and this spectrum is much more like a typical NIR spectrum with broad peaks.

Figure 4 is a spectrum of sucrose, C 12 H 24 O 12 , which shows very broad areas of absorption but also some quite narrow peaks. Read our guide on Where to take your learning next for more information.

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Level 1: Introductory. Course rewards. Free statement of participation on completion of these courses. Ahonen et al developed a portable, real-time FTIR spectrometer as a gas analyzer for industrial hygiene use.

The instrument consists of an operational keyboard, a control panel, signal and control processing electronics, an interferometer, a heatable sample cell and a detector.

All the components were packed into a cart. To minimize the size of the instrument, the resolution of FTIR spectrometer was sacraficed.

But it is good enough for the use of industrial hygiene. Korb et al developed a portable FTIR spectrometer which only weighs about Moreover, the energy source of the instrument is battery so that the mobility is significantly enhanced. Additionally, this instrument resists vibration. It works well in an operating helicopter.

Consequently, this instrument is excellent for the analysis of radiation from the surface and atmosphere of the Earth.

The instrument is also very stable. After a three-year operation, it did not lose optical alignment. The reduction of size was implemented by a creative design of optical system and accessory components.

Two KBr prisms were used to constitute the interferometer cavity. Optical coatings replaced the mirrors and beam splitter in the interferometer. The optical path is shortened with a much more compact packaging of components. A small, low energy consuming interferometer drive was designed. It is also mass balanced to resist vibration. The common He-Ne tube was replaced by a smaller laser diode. The first generation IR spectrometer was invented in late s.

It utilizes prism optical splitting system. The prisms are made of NaCl. Further more, the scan range is narrow. Additionally, the repeatability is fairly poor. As a result, the first generation IR spectrometer is no longer in use. The second generation IR spectrometer was introduced to the world in s. It utilizes gratings as the monochrometer. The performance of the second generation IR spectrometer is much better compared with IR spectrometers with prism monochrometer, But there are still several prominent weaknesses such as low sensitivity, low scan speed and poor wavelength accuracy which rendered it out of date after the invention of the third generation IR spectrometer.

The invention of the third generation IR spectrometer, Fourier transform infrared spectrometer, marked the abdication of monochrometer and the prosperity of interferometer. With this replacement, IR spectrometers became exceptionally powerful. Consequently, various applications of IR spectrometer have been realized. Simplified representation of a dispersive IR spectrometer. Michelson Interferometer The Michelson interferometer, which is the core of FTIR spectrometers, is used to split one beam of light into two so that the paths of the two beams are different.

Schematic of the Michelson interferometer A typical Michelson interferometer consists of two perpendicular mirrors and a beamsplitter. Fourier Transform of Interferogram to Spectrum The interferogram is a function of time and the values outputted by this function of time are said to make up the time domain.

Advantages of Fourier Transform over Continuous-Wave Spectrometry Fourier transform, named after the French mathematician and physicist Jean Baptiste Joseph Fourier, is a mathematical method to transform a function into a new function. IR spectrum of a sample. Sample IR spectrum Step 5: Data analysis is done by assigning the observed absorption frequency bands in the sample spectrum to appropriate normal modes of vibrations in the molecules.

References P. Griffiths, Science , 2 1, , W. Part 1. Topics in Chemical Instrumentation. Frank A. Settle, Jr. Skoog and J. Philadelphia, PA, Chapter Daniels, J. Williams, P. Bender, R. Alberty, C. Cornwell, J. Cooley and J.