SPECTRAL ANALYSIS IN THE UV-VISIBLE RANGE FOR REVEALING THE MOLECULAR FORM OF COMBUSTION-GENERATED CARBONACEOUS SPECIES

摘要

A method of UV-visible spectra analysis was developed for investigating the relationship between the optical properties and the complex composition/structure of carbonaceous species formed in a sooting preim'xed ethylene flame. The UV-visible spectra were measured on carbonaceous species, caught on quartz plates inserted along the flame and recovered by solvent treatment. The contribution and the structure of components in a very wide molecular weight range, from 200 to 1E11 u, were evaluated by size exclusion chromatography coupled with on-line UV-visible spectroscopy of the dichloromethane-soluble and dry soot fractions. The optical band gap and the UV peak position of each MW-segregated fraction were evaluated by means of a spectral deconvolution procedure, to get details on the carbon network structure in terms ofsp~2 and sp~3 sites and size and stacking of the aromatic units.The species included in the 1E8-1E11 u range underwent graphitizationlgrowth reactions during the formation process of carbonaceous species. Large poly cyclic aroamtic hydrocarbon (PAH) molecules and clusters of PAH, included in the 200-1 E8u range, did not exhibit molecular growth and internal structure transformation, suggesting that they merely aggregate/coagulate participating to the formation of carbon particles.