Vibrational Spectroscopies

Stylianos Aspiotis, Olivier Bonnerot, Sebastian Bosch

Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy are widely used analytical methods that can deliver essential information of the chemical composition and structure of crystalline (e.g. minerals) and of amorphous (e.g. glasses) solid materials as well as identify molecules (liquid and aqueous phases), as atomic vibrations are sensitive to both the type and configuration of chemical bonds within a solid or molecule. Vibrational spectroscopies measure the interaction of electromagnetic radiation with the atomic vibrations of the studied materials, as atoms that build up a molecule do not stay stationary, but they vibrate in different ways. These collective atomic vibrations, which can be also called vibrational modes, and their energies are typical of the participating atoms and of the arrangement of those atoms in the analysed molecule or solid. Thus, the application of vibrational spectroscopies identifies the unique “fingerprints” of the molecular and solid phases comprising the material/cultural heritage object under investigation. The biggest advantage of vibrational spectroscopies over other analytical techniques, is the non-destructive and mostly non-invasive (microinvasive in the case of FTIR operating in transmission (see FTIR-Spectrometer Vertex 70, Bruker)) character of these analytical methods, as they operate in reflection mode, and their ability to analyse light-element containing compounds (H-, B-, and C-bearing). However, metals cannot be studied by Raman and FTIR spectroscopies, because, due to the collectivisednature of metal bonding, the probe electromagnetic radiation is totally reflected and penetrate through the sample.