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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Vacuum-UV (172 nm) Actinometry. The Quantum Yield of the Photolysis of Water
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Vacuum-UV (172 nm) Actinometry. The Quantum Yield of the Photolysis of Water

机译：真空紫外（172 nm）光度法。水的光解的量子产率

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With the development of new light sources (Xe-excimer light sources), the vacuum-UV (VUV) photochemistry on a preparative scale is becoming technically feasible. Among the first potential technical applications, VUV photolysis of aqueous systems must be considered as a potential alternative to established "advanced oxidation procedures" (AOP). For the design and dimensioning of corresponding reactors, incident photon rates must be determined. The standard VUV actinometry in condensed phase is the cis-trans isomerization of cyclooctene in n-pentane. The incident photon rate of these new light sources depends on their geometry, the configuration of their electrodes, and the dielectric constant of the solvent in the case where the substrate solution is part of the dielectric barrier; thus actinometric experiments should be made under operational conditions. However, the radiant power density of the excimer sources will be different if n-pentane (standard actinometry) is used as part of the dielectric barrier from when using water (oxidative degradation experiments), because the voltage drop across the fluids is different. Consequently, for projects involving aqueous reactions systems, operational conditions cannot be met by the standard actinometer. Water exhibits a high absorption cross-section for VUV irradiation (λ ＜ 190 nm) and homolyzes mainly into hydroxyl radicals and hydrogen atoms. Hydroxyl radicals, but not hydrogen atoms, are very efficiently scavenged by methanol molecules, and under defined conditions, the rate of production of hydroxyl radicals may be determined from the rate of degradation of methanol dissolved in the aqueous reaction system. The parameters affecting primarily the rate of methanol degradation, i.e., the incident photon rate, the concentration of dissolved molecular oxygen, the initial methanol concentration, and the flow parameters in the photochemical reactor, were determined and optimized for a general actinometric procedure. A normalized diagram of the incident photon rate versus the initial methanol concentration allows one to determine the boundary conditions under which the rate of methanol degradation may be used to evaluate the production rate of hydroxyl radicals for Xe-excimer light sources of different radiant power and independent of their geometry. Having determined both the rate of production of hydroxyl radicals and the rate of methanol degradation, and having calibrated the corresponding incident photon rates by the cis-trans isomerization of cyclooctene (standard actinometry) in an experimental setup in which the emitted photon rate does not depend on the reaction medium, the quantum yield of the homolysis of water by VUV irradiation from Xe-excimer lamps may finally be calculated.
机译：随着新光源（准分子光源）的发展，制备规模的真空紫外（VUV）光化学技术在技术上变得可行。在第一个潜在的技术应用中，必须考虑将水性系统进行VUV光解作为已建立的“高级氧化程序”（AOP）的潜在替代方法。为了设计和确定相应反应堆的尺寸，必须确定入射光子速率。缩合相中标准的VUV光化法是环戊烯在正戊烷中的顺反异构化。这些新光源的入射光子速率取决于它们的几何形状，其电极的配置以及在底物溶液是介电屏障一部分的情况下溶剂的介电常数。因此，应在操作条件下进行光度测定实验。但是，如果使用正戊烷（标准光化法）作为电介质阻挡层的一部分，与使用水（氧化降解实验）时相比，准分子源的辐射功率密度将有所不同，因为流体两端的压降是不同的。因此，对于涉及水反应系统的项目，标准的光度计无法满足操作条件。水在VUV辐照下（λ＜190 nm）具有高吸收截面，并且主要均化为羟基自由基和氢原子。甲醇分子非常有效地清除了羟基自由基，而不是氢原子，在特定条件下，羟基自由基的产生速率可以由溶解在水性反应体系中的甲醇的降解速率来确定。对于一般的光度测定法，确定并优化了主要影响甲醇降解速率的参数，即入射光子速率，溶解的分子氧浓度，初始甲醇浓度和光化学反应器中的流动参数。入射光子速率相对于初始甲醇浓度的归一化图可以确定边界条件，在该条件下甲醇降解速率可用于评估不同辐射功率且独立的Xe准分子光源的羟基自由基产生速率他们的几何形状。确定了羟基自由基的产生速率和甲醇降解的速率，并在不依赖于发射光子速率的实验装置中通过环辛烯的顺反异构化（标准光度法）校准了相应的入射光子速率在反应介质上，最终可以计算出氙气准分子灯通过VUV辐照进行水均质分解的量子产率。

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