Chromophoric Dissolved Organic Matter Photochemistry and Photophysics: Testing the Charge Transfer Model

发色性溶解有机物（CDOM）在水生环境中无处不在，它通过影响水生光场和光化学反应发挥着核心作用。马里兰大学帕克分校（University of Maryland-College Park）的两位研究人员提出，CDOM的光学吸收和发射特性部分源于羟基芳香供体和醌受体之间的分子内电荷转移相互作用，这些相互作用是由可溶性木质素前体的部分氧化形成的（即电荷转移模型）。科学家们提出，电荷转移模型可以在很大程度上解释归因于这种材料的各种光化学反应，并计划使用一系列光化学和光物理测量来验证这一假设，包括以下方面：1)H2O2量子产率对O2浓度及其相关波长的依赖；2)所选（苯酚）供体的氧化速率对O2浓度和供体浓度的依赖关系，以及相关波长的依赖关系；3) O2产率与O2浓度的关系；发射量子产额和寿命的波长依赖性。整套测量将对一种标准（苏瓦尼河黄腐酸）和三种特性良好的水生腐殖质（HS）进行，这些物质是在以前的野外工作中从寡营养、陆架和河口水域收集的。将0.2 m过滤后的整个水样的H2O2产率与O2浓度的光谱依赖性与HS样品进行比较，以量化HS样品的性质在多大程度上反映了原始水的性质。还将进行进一步的测试，检查潜在的关键参数（如pH值、盐度和金属离子含量）的影响。至于更广泛的影响，一名博士后和一名研究生将作为该项目的一部分得到支持和培训。预计本科生也将参与本研究，并了解最新的光化学和光物理方法。

OCE-0648414Chromophoric dissolved organic matter (CDOM) is found ubiquitously in aquatic environments where its plays a central role, both through its impact on the aquatic light field and its photochemical reactions. Two researchers from the University of Maryland-College Park have proposed that optical absorption and emission properties of CDOM arise in part from intramolecular charge transfer interactions between hydroxy-aromatic donors and quinoid acceptors formed by the partial oxidation of soluble lignin precursors (i.e., charge transfer model). The scientists propose that the charge transfer model can largely explain the diverse suite of photochemical reactions attributed to this material and plan to test the hypothesis using a series of photochemical and photophysical measurements including the following: 1) the dependence of H2O2 quantum yields on O2 concentration and its associated wavelength dependence; 2) the dependence of the oxidation rates of selected (phenol) donors on both O2 concentration and donor concentration, as well as the associated wavelength dependencies; 3) the dependence of 1O2 yields on O2 concentrations; and 4) the wavelength dependence of emission quantum yields and lifetimes. The complete suite of measurements will be performed on one standard (Suwanee River fulvic acid) and three well-characterized aquatic humic substances (HS) collected on prior field work from oligotrophic, shelf and estuarine waters. The spectral dependence of the H2O2 yields on O2 concentration for 0.2 M-filtered, whole water samples will be compared to that of the HS samples to quantify the extent to which the properties of the HS samples reflect those of the original waters from which they were obtained. Further tests examining the impact of potentially key parameters such as pH, salinity, and metal ion content will also be conducted.As regards broader impacts, one post doc and one graduate student will be supported and trained as part of this project. It is anticipated that undergraduate students will also participate in this study and learn about state of the art photochemical and photophysical methods.