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

近年来，介质阻挡放电被频繁地研究并用于许多用途，例如环境空气电离和有机分子的软电离。介质阻挡放电也被研究作为替代挥发种雾化器，以取代AAS中常用的外加热石英管雾化器以及AFS中扩散火焰（DF）和气体屏蔽火焰（FIGS）雾化器。它们已被证明是分析光谱的有用工具，因为它们可以作为自由原子、激发态和离子的来源。本项目的主要目标是开发一种能够解离/原子化分子的等离子体，并阐明挥发性物质介质阻挡放电（DBD）的解离机制。一般来说，DBD产生的等离子体的特性很大程度上取决于电极的结构和施加的电压。从应用于软电离源的dbd可知，这些放电可以通过不同的操作模式来区分，因此可以存在均匀模式和丝状模式。用于软电离的DBD应在均匀模式下操作。当DBD用作挥发性物质的雾化器时，哪种操作模式更可取？要回答这个问题，首先需要对等离子体形状进行完全的视觉控制。通常，等离子体在平面dbd中是端对端观察到的。然而，通过这种方式无法获得关于等离子体运行模式的完整信息。因此，将在玻璃上应用具有不同几何形状的透明氧化铟锡（ITO）电极的平面形状DBD，不仅可以观察等离子体的端对端，还可以通过电极表面监测等离子体的发射特性。不同的等离子体设计将应用于吸收和荧光测量。此外，放电电流测量将用于区分两个不同的等离子体，这两个等离子体将暂时分开。时间第一等离子体可以用作软电离等离子体，第二等离子体可以用作解离等离子体。为了确定第二个等离子体是否是解离等离子体，将使用DB等离子体射流，因为电极之间的距离为10mm，比上述构造的放电板之间的距离大4到5倍。因此，可以获得电极之间的时间发射测量值，并与等离子体电流进行比较。为了获得低检测限（LOD）的高效检测，将开发等离子体调制锁相检测。调制等离子体测量将使用氢化硒作为模型分析物和原子吸收和荧光探测器进行。此外，应通过空心阴极灯的强度调制来达到对背景的抑制。

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.