UV excitation of [Fe(H₂O)₆]³⁺ generates hydroxyl radicals in low quantum yield, but the events that compete with this photochemistry are obscure. To elucidate the primary events, acidic, aqueous iron(III) perchlorate solutions were studied by femtosecond pump-probe spectroscopy. We report a new decay channel in which ligand-to-metal charge transfer (LMCT) excitation of [Fe(H₂O)₆]³⁺ hydrolyzes a coordinated water molecule, releasing a proton and forming the iron(III) monohydroxy ion in less than 1 ps. This efficient channel, which is observed here for the first time, competes with hydroxyl radical generation and represents a novel observation of photoacidity in a metal coordination complex.

中文翻译：

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六水合铝离子的超快光化学动力学

[Fe（H ₂ O）₆ ] ^3+的紫外线激发以较低的量子产率产生羟基自由基，但与该光化学竞争的事件却不清楚。为了阐明主要事件，通过飞秒泵浦探针光谱法研究了酸性高氯酸铁（III）水溶液。我们报告了一个新的衰变通道，其中[Fe（H ₂ O）₆ ] ^3+的配体-金属电荷转移（LMCT）激发水解配位的水分子，释放质子并在不到1 ps的时间内形成铁（III）单羟基离子。这是首次在此观察到的有效通道，它与羟基自由基的产生竞争，代表了金属配位络合物中光酸度的新观察。