Mapping extended reaction coordinates in photochemical dynamics
Mapping extended reaction coordinates in photochemical dynamics
复制标题
绘制光化学动力学中的扩展反应坐标
DOI：
10.1016/j.jms.2023.111807
复制
发表时间：
2023
影响因子：
1.4
通讯作者：
Townsend D
中科院分区：
文献类型：
--
作者：
Townsend D
基于激光的实验促进了许多策略，用于询问在分子的激发态中操作的复杂的非绝热动力学。测量可以大致分为频率和时间分辨的变量，通常需要不同方法（具有不同的相关观测值）的组合来揭示完整的机械图。在前一类中，量子态分辨信息通常可以使用窄线宽激光器获得。这提供了与光化学反应坐标上的起始点（通过吸收光谱）和渐近终点（即光产物）有关的详细信息。然而，由于激光脉冲相对于非绝热能量再分布过程的典型时间尺度的固有的长持续时间，连接这两个极限的中间路径的直接观察通常是不可能的。因此，期望获得补充信息，该补充信息在激发态布居穿过势能景观时监测沿着反应坐标的实时演变。这可以在使用超快（即亚皮秒）激光脉冲进行的时间分辨泵浦探测实验中实现。使用价态光电离的探测步骤是一种常用的方法，并已证明在揭示微妙的机制细节的关键能量再分配途径在许多不同的分子系统中运行具有很大的启发性。然而，这里一个常见的限制是沿着连接最初制备的激发态到各种光产物的反应坐标的受限“视图”沿着。从最近的工作中使用时间分辨光电子成像的例子的指导下，本次审查将详细讨论这些问题，并强调一些策略，可能有助于克服它们-特别强调尽可能深入到电离连续投影的优势。还将加强使用其他光谱技术的补充测量的作用以及高水平支持理论对指导数据解释的重要性。
Laser-based experiments facilitate numerous strategies for interrogating the complex non-adiabatic dynamics operating in the excited states of molecules. Measurements may be broadly separated into frequency- and time-resolved variants, with a combination of different approaches (with different associated observables) typically being required to reveal a complete mechanistic picture. In the former category, quantum state-resolved information may often be obtained using narrow linewidth lasers. This provides detailed information relating to the starting point on the photochemical reaction coordinate (via the absorption spectrum) and the asymptotic endpoints (i.e. the photoproducts). Direct observation of the intermediate pathways connecting these two limits is often not possible, however, due to the inherently long temporal duration of the laser pulses relative to the typical timescales of non-adiabatic energy redistribution processes. It is therefore desirable to obtain complementary information that monitors real-time evolution along the reaction coordinate as excited state population traverses the potential energy landscape. This may be achieved in time-resolved pump–probe experiments conducted using ultrafast (i.e. sub-picosecond) laser pulses. The use of valence state photoionization for the probe step is a commonly employed methodology and has proved highly instructive in revealing subtle mechanistic details of key energy redistribution pathways operating in many different molecular systems. One frequent limitation here, however, is the restricted “view” along the reaction coordinate(s) connecting the initially prepared excited states to various photoproducts. Guided by examples drawn from recent work using time-resolved photoelectron imaging, this review will discuss such issues in detail and highlight some strategies that potentially help overcome them – with particular emphasis placed on the advantages of projecting as deeply as possible into the ionization continuum. The role of complementary measurements using other spectroscopic techniques and the importance of high-level supporting theory to guide data interpretation will also be reinforced.