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首页> 美国卫生研究院文献>Structural Dynamics >Ultraviolet photochemical reaction of Fe(III)(C2O4)33− in aqueous solutions studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser
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Ultraviolet photochemical reaction of Fe(III)(C2O4)33− in aqueous solutions studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser

机译：飞秒时间分辨X射线吸收光谱法使用X射线自由电子激光研究Fe（III）（C2O4）3 3-在水溶液中的紫外光化学反应

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Time-resolved X-ray absorption spectroscopy was performed for aqueous ammonium iron(III) oxalate trihydrate solutions using an X-ray free electron laser and a synchronized ultraviolet laser. The spectral and time resolutions of the experiment were 1.3 eV and 200 fs, respectively. A femtosecond 268 nm pulse was employed to excite [Fe(III)(C2O4)3]3− in solution from the high-spin ground electronic state to ligand-to-metal charge transfer state(s), and the subsequent dynamics were studied by observing the time-evolution of the X-ray absorption spectrum near the Fe K-edge. Upon 268 nm photoexcitation, the Fe K-edge underwent a red-shift by more than 4 eV within 140 fs; however, the magnitude of the redshift subsequently diminished within 3 ps. The Fe K-edge of the photoproduct remained lower in energy than that of [Fe(III)(C2O4)3]3−. The observed red-shift of the Fe K-edge and the spectral feature of the product indicate that Fe(III) is upon excitation immediately photoreduced to Fe(II), followed by ligand dissociation from Fe(II). Based on a comparison of the X-ray absorption spectra with density functional theory calculations, we propose that the dissociation proceeds in two steps, forming first [(CO2•)Fe(II)(C2O4)2]3− and subsequently [Fe(II)(C2O4)2]2−.
机译：使用X射线自由电子激光和同步紫外激光对草酸三水合草酸铵铁（III）水溶液进行时间分辨X射线吸收光谱分析。实验的光谱和时间分辨率分别为1.3 eV和200 fs。飞秒268 nm脉冲用于激发溶液中的[Fe（III）（C2O4）3] 3-从高旋转地电子态到配体到金属的电荷转移态，然后通过观察Fe K边缘附近X射线吸收光谱的时间演化来研究随后的动力学。在268 nm的光激发下，Fe K边在140 fs内发生了红移超过4 eV。但是，红移的幅度随后在3 ps内减小。光产物的Fe K边缘的能量仍然低于[Fe（III）（C2O4）3] sup-3-。观察到的Fe K边缘的红移和产物的光谱特征表明，Fe（III）激发后立即被光还原为Fe（II），然后从Fe（II）上解离配体。基于X射线吸收光谱与密度泛函理论计算的比较，我们建议离解过程分两个步骤进行，首先形成[[CO2 •] Fe（II）（C2O4）2] 3-，然后是[Fe（II）（C2O4）2] 2-。

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