Continuous process of the vacuum ultraviolet- (VUV-) photochemical oxidation of thiophene in the gas phase

Thiophene was taken as a model compound for investigations on the efficiency of a continuous process of the vacuum-ultraviolet- (VUV-) photochemically initiated oxidation and mineralization of sulfur containing organic compounds in the gas phase. In the presence of molecular oxygen, atomic oxygen and ozone were photochemically generated and are assumed to initiate or participate in the (thermal) oxidation network. Addition of water vapor for an additional initiation of the oxidation by hydroxyl radicals did not accelerate the process. For comparison, thiophene was exposed to ozone and oxidized under otherwise the same experimental conditions, but complete mineralization was only found in the photochemical process and for relatively small concentrations of the substrate. The result may be explained by low rates of secondary thermal reactions of a number of identified intermediate products. Combining already published results and mechanistic hypotheses with the results of the present work, pathways of oxidative degradation are proposed. The photolysis of thiophene in molecular nitrogen confirmed earlier findings.