Elucidation of dissociation mechanisms of a dielectric barrier discharge for volatile species

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In recent years, dielectric barrier discharges are frequently investigated and used for many purposes as, for instance, for ambient air ionization and soft ionization of organic molecules. Dielectric barrier discharges have also been investigated as alternative volatile species atomizers to replace the commonly used externally heated quartz tube atomizers in AAS as well as diffusion flames (DF) and flame-in-gas-shield (FIGS) atomizers in AFS. They have been proven as useful tools in analytical spectrometry since they may serve as a source of free atoms, excited species as well as ions. The main goal of this project is to develop a plasma capable of dissocia-tion/atomization of molecules and to elucidate dissociation mechanisms of a dielec-tric barrier discharge (DBD) for volatile species. In general, the properties of the plasmas generated by DBD strongly depend on electrode configuration and applied voltages. It is known from DBDs applied as soft ionization source that these discharges can be distinguished by different modes of operation, thus homogeneous and fila-mentary modes can exist. The DBD used for soft ionization should be operated in a homogeneous mode. Which mode of operation might be preferable when the DBD is applied as atomizer for volatile species? To answer this question, first of all a complete visual control of the plasma shape is necessary. Usually, the plasma is end-on observed in planar DBDs. However, no complete information about the operation mode of the plasma can be obtained in this manner. As a consequence, a planar shaped DBD with transparent Indium Tinn Oxide (ITO) electrodes of different geometries on glass will be applied in order not to see the plasma end-on only, but also to monitor the plasma emission characteristics along the electrodes through their surface. Different plasma designs will be applied for absorption and fluorescence measurements. Furthermore, discharge current measurements will be used to distinguish two different plasmas which will be temporally separated. The temporal first plasma might be the plasma which can be used for soft ionisation and the second the one which can be applied as dissociative plasma. In order to find out if the second plasma is the dissociative one a DB plasma-jet will be used because the distance of the electrodes is with 10 mm 4 to 5 times bigger than that of the distance in between the plates of the above constructed discharges. Therefore, temporal emission measurements in between the electrodes can be ob-tained and compared with the plasma currents. A plasma modulated lock-in detection will be developed in order to obtain an efficient detection with low detection limit (LOD). Modulated plasma measurements will be performed using Se hydride as model analyte and atomic absorption and fluorescence detectors. Additionally, a suppression of the background should be reached by intensity modulation of the hollow cathode lamp.