基于液体束光电子影像技术的水合电子激发态动力学研究

Hydrated electron plays an important role in physical chemistry, bio-chemistry and life science. However, its excited-state dynamics was under debate over the past decades. Very recently, after the developing of photoelectron spectroscopy of liquid beam, one can study the dynamics in liquid phase under vacuum for the first time. Using this advanced technique, the decay dynamics of excited-state hydrated electron was revealed and thus the debate was settled. However, in the initial stage (<75fs), it is mostly likely that the decay of the excited-state wavepacket proceed along with its internal conversion process. Since the photoelectron will red shifted both in excited-state wavepacket decays and the internal conversion process, it’s hard to tell whether they proceed sequentially or parallelly only using the photoelectron spectroscopy of liquid beam. Therefore, we propose to reveal this puzzle using photoelectron imaging spectroscopy of liquid beam with time-resolution as high as 40fs. More importantly, photoelectron imaging provide angular distribution of the electron in addition to its kinetic energy distribution. Since the ground state is an s state and the excited state is a p state, the angular distribution of the photoelectrons will be different between these two states. With this new information, we can determine whether these two channels proceed sequentially or parallelly. Besides, we also plan to study the decay dynamics of excited solvent electron in different solvents, such as methanol and ethanol. This study will provide deeper understanding of the nature of hydrated electron.

水合电子在物理化学、生物化学以及生命科学中具有极其重要的作用。然而，其激发态的特性在过去的几十年里一直存在争议。近年来，随着液体束光电子能谱技术的引入，人们首次能够在真空环境中对液相动力学进行研究,并成功的解决了水合电子激发态演化的模型之争。然而，在极短时间尺度内（<75fs），水合电子激发态波包的演化与内转换过程极可能同时进行。由于在这两个过程中光电子能谱的峰值大小和移动趋势相似，因此，仅利用光电子能谱无法进行区分。鉴于此，本项目拟采用时间分辨率约40fs的液体束光电子影像技术来解答此疑惑。更高的时间分辨率将提供更加准确的时间常数，更重要的是光电子影像技术能够同时提供光电子能量和角度分布的信息。利用水合电子激发态和基态的光电子角度分布的不同，我们将呈现更全面的激发态演化机理。同时，我们还将讨论不同溶液对电子激发态动力学的影响，研究其溶剂效应。本课题的开展将提高人们对水合电子本质的认识。