Within the scope of material analysis, spectroscopic recordings are frequently carried out in addition to DSC analyses and density determinations. IR spectroscopy is a method for qualitative analysis.
It is used for structure elucidation and identification of molecules and characteristic atomic groups. In this method, atomic groups are excited in a wavelength range from 2.5 µm to 25 µm using infrared radiation. In this process, certain atomic groups and molecules interact only with very specific wavelengths, i.e. specific energies. Molecules can absorb energy or re-emit it in the form of electromagnetic radiation. In the IR spectrum, the transmission of radiation is often expressed as a function of wavenumber (wavenumber = reciprocal wavelength). The representation as absorption spectrum is mainly used in the ATR technique. The wavenumber range in classical IR spectroscopy is from 4000 cm-1 to 400 cm-1.
In the evaluation, the exact wavenumbers as well as the intensity of the bands are considered. For the evaluation of the usually very complex spectra, databases with comparison spectra are used. Compared to transmission spectroscopy, ATR spectroscopy is mainly used for the surface examination of opaque materials (e.g. polymer films or paints).