Raman spectroscopy as tool for the characterization of thio-polyaromatic hydrocarbons in organic minerals

Benzothiophene and dibenzothiophene have been studied by Raman microspectroscopy using a 785 nm excitation wavelength. The spectra obtained have been compared with the previously measured spectra of idrialite, a complex natural mineral composed entirely of cata-condensed polyaromatic hydrocarbons (PAHs), usually containing a thiophenic or aliphatic five-membered ring. For comparison, the Raman spectra of 2,3-benzofluorene crystals have been obtained for the first time. Some of the bands in the idrialite spectra are attributed to specific vibrational modes of thiophene or fluorene-type PAHs, especially in the region bellow 1000 cm−1. These modes at 495, 705 and 750 cm−1 along with C–H or C–H2 stretching modes around 3000 cm−1 can be then used to distinguish such groups of PAHs in complicated organic mineral mixtures like idrialite.