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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electron photodetachment from aqueous anions. 3. Dynamics of geminate pairs derived from photoexcitation of mono- vs polyatomic anions
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Electron photodetachment from aqueous anions. 3. Dynamics of geminate pairs derived from photoexcitation of mono- vs polyatomic anions

机译：电子与水性阴离子的光分离。 3.由单原子和多原子阴离子的光激发得到的双峰对动力学

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Photostimulated electron detachment from aqueous inorganic anions is the simplest example of solvent-mediated electron transfer reaction. As such, this photoreaction became the subject of many ultrafast studies. Most of these studied focused on the behavior of halide anions, in particular, iodide, that is readily accessible in the UV. In this study, we contrast the behavior of these halide anions with that of small polyatomic anions, such as pseudohalide anions ( e. g., HS-) and common polyvalent anions ( e. g., SO32-). Geminate recombination dynamics of hydrated electrons generated by 200 nm photoexcitation of aqueous anions (I-, Br-, OH-, HS-, CNS,- CO32-, SO32-, and Fe(CN)(6)(4-)) have been studied. Prompt quantum yields for the formation of solvated, thermalized electrons and quantum yields for free electrons were determined. Pump-probe kinetics for 200 nm photoexcitation were compared with kinetics obtained at lower photoexcitation energy ( 225 or 242 nm) for the same anions, where possible. Free diffusion and mean force potential models of geminate recombination dynamics were used to analyze these kinetics. These analyses suggest that for polyatomic anions ( including all polyvalent anions studied) the initial electron distribution has a broad component, even at relatively low photoexcitation energy. There seems to be no well-defined threshold energy below which the broadening of this electron distribution does not occur, as is the case for halide anions. The constancy of (near-unity) prompt quantum yields vs the excitation energy as the latter is scanned across the lowest charge-transfer-to-solvent band of the anion is observed for halide anions but not for other anions: the prompt quantum yields are considerably less than unity and depend strongly on the excitation energy. Our study suggests that halide anions are in the class of their own; electron photodetachment from polyatomic, especially polyvalent, anions exhibits qualitatively different behavior.
机译：从含水无机阴离子进行光刺激的电子脱离是溶剂介导的电子转移反应的最简单例子。因此，这种光反应成为许多超快研究的主题。这些研究大多数集中在紫外线中容易接近的卤化物阴离子，特别是碘化物的行为。在这项研究中，我们将这些卤化物阴离子与小的多原子阴离子，例如假卤化物阴离子（例如HS-）和常见的多价阴离子（例如SO32-）的行为进行对比。通过200 nm光激发含水阴离子（I-，Br-，OH-，HS-，CNS，-CO32-，SO32-和Fe（CN）（6）（4-））产生的水合电子的Geate重组动力学具有经过研究。确定了形成溶剂化，热化电子的迅速量子产率和自由电子的量子产率。在可能的情况下，将200 nm光激发的泵浦探针动力学与在较低光激发能量（225或242 nm）下获得的动力学进行了比较。自由基重组动力学的自由扩散和平均力势模型用于分析这些动力学。这些分析表明，对于多原子阴离子（包括所有研究的多价阴离子），即使在相对较低的光激发能下，其初始电子分布也具有较宽的分量。似乎没有明确定义的阈值能量，低于该阈值能量就不会发生这种电子分布的扩展，就像卤化物阴离子的情况一样。 （近一）瞬态量子产率的恒定性与激发能的关系，因为在卤化物阴离子的最低电荷转移至溶剂的整个能带范围内扫描激发能，而对其他阴离子则观察不到：瞬态量子产率为远小于统一，并且很大程度上取决于激发能。我们的研究表明，卤化物阴离子属于它们自己的类别。电子与多原子阴离子（尤其是多价阴离子）的光脱附表现出质的不同行为。

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