Department of Chemistry , Durham University , Durham DH1 3LE , U.K.
J Phys Chem B. 2019 Mar 14;123(10):2373-2379. doi: 10.1021/acs.jpcb.8b11766. Epub 2019 Feb 27.
The photo-oxidation dynamics following ultraviolet (257 nm) excitation of the phenolate anion in aqueous solution is studied using broadband (550-950 nm) transient absorption spectroscopy. A clear signature from electron ejection is observed on a sub-picosecond timescale, followed by cooling dynamics and the decay of the signal to a constant offset that is assigned to the hydrated electron. The dynamics are compared to the charge-transfer-to-solvent dynamics from iodide at the same excitation wavelength and are shown to be very similar to these. This is in stark contrast to a previous study on the phenolate anion excited at 266 nm, in which electron emission was observed over longer timescales. We account for the differences using a simple Marcus picture for electron emission in which the electron tunneling rate depends sensitively on the initial excitation energy. After electron emission, a contact pair is formed which undergoes geminate recombination and dissociation to form the free hydrated electron at rates that are slightly faster than those for the iodide system. Our results show that, although the underlying chemical physics of electron emission differs between iodide and phenolate, the observed dynamics can appear very similar.
采用宽带（550-950nm）瞬态吸收光谱研究了水溶液中酚盐阴离子在紫外（257nm）激发下的光氧化动力学。在亚皮秒时间尺度上观察到了电子发射的明显特征，随后是冷却动力学和信号衰减到一个恒定的偏移，该偏移被分配给水合电子。将动力学与相同激发波长下碘化物的电荷转移到溶剂的动力学进行了比较，结果表明它们非常相似。这与之前在 266nm 激发下研究酚盐阴离子的研究形成鲜明对比，在该研究中观察到电子发射的时间尺度更长。我们使用电子发射的简单马库斯图像来解释这些差异，其中电子隧穿率对初始激发能量敏感。电子发射后，形成一个接触对，该对经历复合和离解，以比碘化物体系稍快的速率形成自由水合电子。我们的结果表明，尽管碘化物和酚盐之间电子发射的基础化学物理性质不同，但观察到的动力学可能非常相似。
