XPS AND NEXAFS SYNCHROTRON SPECTROSCOPY OF PAH RELEVANT IN COMBUSTION AND ENVIRONMENT FIELD

Detailed information on the chemical and physical structure of the nanometric carbon species accompanying soot formation and emission are important to assess their possible health and environmental effects as well as to identify the pathways involved in soot inception and growth. Consequently, there is an increasing demand for diagnostic techniques capable to determine properties of nanoparticles not easily accessible to traditional analytical methods. The present work aims to contribute in developing a new analytical approach with synchrotron radiation for the analysis of PAH that, beside to be emitted as individual molecules, mimic the basic units (aromatic layers) of fine and ultrafine particles. Some PAH standards, selected among the most abundant combustion-formed PAH, have been suitably volatilized and on-line analysed in gas phase. Their electronic structures have been studied by means of synchrotron radiation spectroscopy at the carbon K-edge: X-ray Photoelectron spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure (NEXAFS). The XPS spectra of the standard molecules have been measured in order to determine the C1s ionization potentials. The molecules under study have many non-equivalent carbon atoms, which are expected to produce several overlapping C 1s photoelectron lines. The C1s band characteristics have been studied and correlated with the PAH structure, which differs in the rings number, condensation degree, five-ring presence. The XPS data were matched with the NEXAFS ones for achieving information also about the local environment around a specific type of absorber atom. On the basis of the findings obtained from the experiments on PAH in gas phase, some insights on the C1s band of XPS spectrum of combustion-formed soot particles were given too.