Carbon K-edge X-ray Raman spectroscopy supports simple, yet powerful description of aromatic hydrocarbons and asphaltenes

The nature and distribution of electron density in polycyclic aromatic hydrocarbons (PAHs) determines PAH properties. Theoretical investigations have yielded simple heuristics to describe the pi electron distribution in complex PAHs, but systematic experimental support is lacking. Here, we show that using the novel approach of carbon K-edge X-ray Raman spectroscopy (XRRS), carbon type in PAHs can be probed directly. Our unique detector has enabled application of XRRS on PAHs and asphaltenes. XRRS results directly support the powerful 'aromatic sextet' description of PAHs. Also, XRRS is shown to establish geometries of aromatic ring systems in asphaltenes, a complex natural carbonaceous material. (C) 2003 Elsevier Science B.V. All rights reserved.