Raman Spectroscopy of Mineral Oil Products. Part I: NIR/FT-Raman Spectra of Polycyclic Aromatic Hydrocarbons

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are regarded as belonging to the most hazardous compounds in some exhaust gases. Their identification has been difficult since most analytical methods suffer from low specifity or low sensitivity. Raman spectra of polycyclic aromates are expected to show typical fingerprint patterns. However, they could not be recorded with excitation in the visible range of the spectrum since fluorescence was excited instead, with a quantum yield several orders of magnitude larger. The great advantage of the new NIR/FT-Raman spectroscopy is that fluorescence of most compounds cannot be excited, because the energy of the exciting light quanta at 1064 nm is only 46% of the quanta at 488 nm. This paper demonstrates that polycyclic aromates with 4 to 7 rings show very strong and sharp Raman lines. Their distinct patterns supply a powerful tool for identification and multicomponent analyses of PAHs.