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

OCE-0648414有色溶解有机物（CDOM）在水生环境中无处不在，通过其对水生光场和光化学反应的影响，它在其中发挥着核心作用。 来自马里兰大学帕克分校的两名研究人员提出，CDOM的光吸收和发射性质部分源于羟基芳族供体和醌型受体之间的分子内电荷转移相互作用，所述羟基芳族供体和醌型受体通过可溶性木质素前体的部分氧化形成（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测试这一假设，包括：1）H2 O2量子产率对O2浓度的依赖性及其相关的波长依赖性; 2）所选（苯酚）供体的氧化速率对O2浓度和供体浓度的依赖性以及相关的波长依赖性; 3）1 O2产率对O2浓度的依赖性;以及4）发射量子产率和寿命的波长依赖性。 完整的测量套件将进行一个标准（苏瓦尼河富里酸）和三个良好的特点水生腐殖物质（HS）收集在贫营养，货架和河口沃茨的前期实地工作。将0.2 M过滤的全水样品的H2 O2产率对O2浓度的光谱依赖性与HS样品的光谱依赖性进行比较，以量化HS样品的性质反映它们从中获得的原始沃茨的性质的程度。此外，还将进一步测试pH值、盐度和金属离子含量等潜在关键参数的影响。关于更广泛的影响，作为该项目的一部分，将支持和培训一名博士后和一名研究生。 预计本科生也将参与这项研究，并了解最先进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.