Fluorescence spectroscopic study of reactions between gaseous ozone and surface-adsorbed polycyclic aromatic hydrocarbons

Abstract

Kinetics of reactions between gaseous ozone (O/sub 3/) and two polycyclic aromatic hydrocarbons (PAH), perylene and benzo(a)pyrene (BaP), adsorbed on fused silica plates were studied by observation of PAH fluorescence spectra as functions of PAH concentration, reaction time, and O/sub 3/ concentration. Significant improvement of the fluorescence signal to scattered light ratio was achieved by using small-angle edge-on illumination configuration. In addition, the photoinduced reactions of PAH by excitation light was minimized. The PAH in aggregated states, as inferred from the excimer fluorescence, exhibited a much slower reaction with O/sub 3/ than those in dispersed forms. With highly dispersed samples, the decays were exponential and the rates proportional to O/sub 3/ concentrations. From these data, the second-order rate constants were determined with the corresponding half-lives of 132 and 2.6 min in 0.2 ppm of O/sub 3/ for perylene and BaP, respectively.