Physik-Department E 11, Technische Universität München, D-85748 Garching, Germany.
Phys Chem Chem Phys. 2009 Dec 14;11(46):10939-44. doi: 10.1039/b913688f. Epub 2009 Sep 30.
The photodetachment of aqueous bromide after excitation at 202 nm is studied by pump-probe and pump-repump-probe spectroscopy. The initially excited charge-transfer-to-solvent state is followed by an intermediate assigned to non-equilibrated bromine-electron pairs. The subsequent dynamics are governed by equilibration, recombination and dissociation of the pairs, yielding the final hydrated electrons. An additional repump pulse is used for secondary excitation of the intermediate species, increasing the final number of hydrated electrons. Thus, a fraction of the solvent-separated bromine-electron pairs are converted to fully released electrons representing an optical manipulation of the photodetachment pathway. The observed hindrance of the recombination process by repumping allows determination of the effective lifetime of the solvent-separated atom-electron pairs to be 19 +/- 2 ps at room temperature. The measured temperature dependence of the time constant suggests a free energy barrier for pair dissociation of DeltaG = 0.15 +/- 0.02 eV.
本文通过泵浦-探测和泵浦-重泵-探测光谱法研究了 202nm 激发后水合溴化物的光电子分离。最初激发的电荷转移到溶剂态后，会出现一个中间态，其被分配给非平衡的溴-电子对。随后的动力学过程受电子对的平衡、复合和离解的控制，生成最终的水合电子。通过使用额外的重泵脉冲对中间态进行二次激发，可以增加最终的水合电子数量。因此，一部分溶剂分离的溴-电子对被转化为完全释放的电子，这代表对光电子分离途径的光学控制。通过重泵来抑制复合过程，可以确定室温下溶剂分离原子-电子对的有效寿命为 19±2 ps。测量得到的时间常数的温度依赖性表明，对电子对离解的自由能势垒为 DeltaG=0.15±0.02 eV。
