The infrared spectroscopy is a method of the vibrational spectroscopy and is used for the characterisation of materials.
With infrared spectroscopy, radiation in the range of middle infrared (MIR) – indicated as reciprocal of the wavelength, the so-called wave number (cm-1) – is irradiated into a substance. The wave number amounts to several 100 up to several 1.000 cm-1
The material absorbs some of the wavelength, since its energies excite the vibration of particular molecule groups. In the spectrum registered, absorption bands can be found at these energies. The infrared spectrum is like a fingerprint characteristic for the molecule analysed and can be used for example for the identification of substances.
The most common construction type of an infrared spectrometer today is the Fourier-transform (FT-) IR-spectrometer, which uses a Michelson-interferometer for the analysis of the signal.
Another method still frequently applied today is the “attenuated total reflection”, which enables a simple sampling for solids and fluids.