Nonadiabatic Dynamics Studied by Liquid-Jet Time-Resolved Photoelectron Spectroscopy
Nonadiabatic Dynamics Studied by Liquid-Jet Time-Resolved Photoelectron Spectroscopy
复制标题
通过液体喷射时间分辨光电子能谱研究非绝热动力学
DOI：
10.1021/acs.accounts.2c00609
复制
发表时间：
2022
影响因子：
18.3
通讯作者：
Neumark, Daniel M.
中科院分区：
文献类型：
--
作者：
Heim, Zachary N.;Neumark, Daniel M.
fabel及其同事开发的液体微射流技术使得利用高真空方法研究高蒸汽压液体和溶液成为可能。其中一种方法是光电子能谱（PES），它允许人们以特定状态的方式通过电离来探测样品的电子特性。由纯溶剂和溶质-溶剂体系组成的液体微射流已经在利用PES和最近的时间分辨PES （TRPES）的研究中取得了巨大成功。在这里，我们讨论了近年来使用这些方法在理解溶剂化电子和核酸组分（nac）的溶剂化和激发态动力学方面取得的进展，以及对它们未来的展望。溶剂化电子在液体微射流实验中是特别有趣的，因为它代表了最简单的溶质体系。尽管如此简单，但它的结合能和激发态弛豫动力学仍有许多未解决的问题，这些问题是液体微射流PES的理想问题。在本报告讨论的工作中，精确地测量了多种高蒸气压溶剂中溶剂化电子的结合能。液体射流PES的优势在对水中溶剂化电子的飞秒激发态弛豫研究中得到进一步突出，其中测量到从激发态到热基态的内部转换导致的75±20 fs的寿命，支持非绝热弛豫机制。核酸成分代表了一类重要的溶质，有几个未解决的问题，液体微射流PES方法是唯一适合解决的。由于TRPES能够跟踪具有状态特异性的动态，因此它非常适合动态中可能涉及多个激发态的情况。利用紫外光对NAC激发后的弛豫进行时间分辨研究，确定了多个激发态的弛豫寿命。TRPES方法的状态特异性使我们能够确定胸腺嘧啶衍生的NACs中缺乏任何可归因于1nπ*状态的信号。该技术的飞秒时间分辨率也有助于识别胸腺嘧啶和单磷酸胸腺嘧啶激发态寿命之间的差异。在分子动力学模拟的帮助下，这些被解释为构象差异的影响，导致单磷酸胸苷的激发态寿命更长。最后，我们讨论了桌面光源扩展到极紫外和软x射线的进展，这些进展允许将液体射流TRPES扩展到全价带，并可能在液体微射流中对溶质和纯液体进行核心水平的研究。由于大多数溶质的基态结合能在10 eV范围内，使用紫外泵浦-紫外探针TRPES观察激发态衰变和基态恢复一直是棘手的。使用高谐波产生的光源，不仅可以观察价能级动力学的完整松弛路径，而且可以通过探测感兴趣的溶质的核心能级来跟踪元素特异性的动力学。
ConspectusThe development of the liquid microjet technique by Faubel and co-workers has enabled the investigation of high vapor pressure liquids and solutions utilizing high-vacuum methods. One such method is photoelectron spectroscopy (PES), which allows one to probe the electronic properties of a sample through ionization in a state-specific manner. Liquid microjets consisting of pure solvents and solute–solvent systems have been studied with great success utilizing PES and, more recently, time-resolved PES (TRPES). Here, we discuss progress made over recent years in understanding the solvation and excited state dynamics of the solvated electron and nucleic acid constituents (NACs) using these methods, as well as the prospect for their future.The solvated electron is of particular interest in liquid microjet experiments as it represents the simplest solute system. Despite this simplicity, there were still many unresolved questions about its binding energy and excited state relaxation dynamics that are ideal problems for liquid microjet PES. In the work discussed in this Account, accurate binding energies were measured for the solvated electron in multiple high vapor pressure solvents. The advantages of liquid jet PES were further highlighted in the femtosecond excited state relaxation studies on the solvated electron in water where a 75 ± 20 fs lifetime attributable to internal conversion from the excited p-state to a hot ground state was measured, supporting a nonadiabatic relaxation mechanism.Nucleic acid constituents represent a class of important solutes with several unresolved questions that the liquid microjet PES method is uniquely suited to address. As TRPES is capable of tracking dynamics with state-specificity, it is ideal for instances where there are multiple excited states potentially involved in the dynamics. Time-resolved studies of NAC relaxation after excitation using ultraviolet light identified relaxation lifetimes from multiple excited states. The state-specific nature of the TRPES method allowed us to identify the lack of any signal attributable to the1nπ* state in thymine derived NACs. The femtosecond time resolution of the technique also aided in identifying differences between the excited state lifetimes of thymidine and thymidine monophosphate. These have been interpreted, aided by molecular dynamics simulations, as an influence of conformational differences leading to a longer excited state lifetime in thymidine monophosphate.Finally, we discuss advances in tabletop light sources extending into the extreme ultraviolet and soft X-ray regimes that allow expansion of liquid jet TRPES to full valence band and potentially core level studies of solutes and pure liquids in liquid microjets. As most solutes have ground state binding energies in the range of 10 eV, observation of both excited state decay and ground state recovery using ultraviolet pump–ultraviolet probe TRPES has been intractable. With high-harmonic generation light sources, it will be possible to not only observe complete relaxation pathways for valence level dynamics but to also track dynamics with element specificity by probing core levels of the solute of interest.