Controlling photophysics and photochemistry via quantum superpositions of electronic states: towards attochemistry

通过电子态的量子叠加控制光物理和光化学：走向原子化学

基本信息

批准号：
EP/T006560/1
负责人：
Graham Worth
金额：
$ 61.1万
依托单位：
University College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2020
资助国家：
英国
起止时间：
2020 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FT006560%2F1
关键词：
Controlling photophysics photochemistry via quantum

项目摘要

When molecules absorb light of sufficient energy, an excited electronic state is generated. The distribution of electrons - the chemical bonding - then changes, causing the nuclei to move in response. Electronic changes such as these appear to be instantaneous relative to the nuclear motion that follows. We now know that these electronic changes aren't instantaneous, but they are usually much faster than the nuclear motions, which has limited our scope for controlling their effects until now.We propose to explore how laser manipulation of electronic state motion can offer unprecedented control over photochemistry: chemical reactions that are initiated by changes in bonding in electronic excited states. Can we direct the outcome of a photochemical process in a molecule by controlling the initial evolution of a coherent quantum superposition of its electronic states? Our proposed research will explore a new approach to controlling dynamics in molecular systems at an important interdisciplinary junction. It promises to benefit our understanding of - and mastery over - ultrafast chemical processes, and to extend our ability to manipulate quantum states of matter into the attosecond time domain.Recently attosecond molecular physics has been exploring the concept of "charge migration": electronic dynamics following sudden excitation of an electron in a molecule or other extended quantum system. To understand such phenomena we must recognise the quantum nature of both electrons and nuclei. Ultrafast decoherence due to coupling of the evolving electronic and nuclear quantum states is found to be rapid and general, taking place on a timescale of a few tens of femtoseconds. The control of photoexcited quantum state dynamics can therefore only be achieved with light fields applied on a faster timescale, before decoherence removes our scope for control. A central target of this research is the control of quantum evolution by ultrafast light fields in the vicinity of conical intersections: molecular geometries where crossings between electronic states can lead to multiple chemical pathways. Control here will give us control over different chemical outcomes. Excitation-control-probe sequences of light pulses will be applied to selected molecules. A few-femtosecond UV excitation pulse will initiate the electronic state superposition, followed by a few-cycle infrared pulse after a short and precisely controlled time delay. This pulse sequence will manipulate the coherence between states as the system flows through the critical conical intersection. By varying the superposition within a time interval of a few tens of femtoseconds in this way - on a time-scale faster than decoherence - we will change the quantum evolution path and final outcomes. This path will be measured in real-time via X-ray spectroscopy with sub-femtosecond X-ray pulses, a technique with a high sensitivity to molecular structure and electronic states. Computer simulations using state-of-the-art codes and substantial computing power to solve the coupled electronic-nuclear motions will be used both to predict and to explain the experiments.We will study the dynamics and control of small, isolated, molecular systems in this proposal. Nevertheless, it is likely that what we will learn through this research will be applicable to the quantum scale manipulation of many other light-absorbing systems with ultrafast chemical dynamics. This work is therefore pertinent to a wide range of nanoscale systems: nanoparticles, catalytic complexes, biomolecules, organic optoelectronics, two-dimensional materials and other advanced materials. As well as providing new insight into the fundamental behaviour of molecules, the ultrafast quantum science we are researching may lead to future quantum devices where the flow of charge, energy and information within a quantum system can be controlled by ultrafast light fields.

当分子吸收足够能量的光时，就会产生激发电子态。然后电子的分布（化学键）发生变化，导致原子核做出响应而移动。诸如此类的电子变化相对于随后的核运动似乎是瞬时的。我们现在知道这些电子变化不是瞬时的，但它们通常比核运动快得多，这限制了我们迄今为止控制其影响的范围。我们建议探索电子态运动的激光操纵如何提供前所未有的控制光化学：由电子激发态键合变化引发的化学反应。我们能否通过控制分子电子态相干量子叠加的初始演化来指导分子光化学过程的结果？我们提出的研究将探索一种在重要的跨学科交叉点控制分子系统动力学的新方法。它有望有助于我们理解和掌握超快化学过程，并将我们操纵物质量子态的能力扩展到阿秒时域。最近，阿秒分子物理学一直在探索“电荷迁移”的概念：电子动力学分子或其他扩展量子系统中的电子突然激发后。为了理解这些现象，我们必须认识电子和原子核的量子性质。由于不断演化的电子和核量子态的耦合而导致的超快退相干被发现是快速且普遍的，发生在几十飞秒的时间尺度上。因此，在退相干消除我们的控制范围之前，只能通过在更快的时间尺度上应用光场来实现光激发量子态动力学的控制。这项研究的一个中心目标是通过圆锥形交叉点附近的超快光场来控制量子演化：在分子几何结构中，电子态之间的交叉可以导致多种化学途径。此处的控制将使我们能够控制不同的化学结果。光脉冲的激发控制探针序列将应用于选定的分子。几飞秒紫外激发脉冲将启动电子态叠加，然后在短暂且精确控制的时间延迟后发出几周期红外脉冲。当系统流过临界圆锥形交叉点时，该脉冲序列将操纵状态之间的相干性。通过以这种方式在几十飞秒的时间间隔内改变叠加——在比退相干更快的时间尺度上——我们将改变量子演化路径和最终结果。该路径将通过使用亚飞秒 X 射线脉冲的 X 射线光谱进行实时测量，这是一种对分子结构和电子态具有高灵敏度的技术。使用最先进的代码和强大的计算能力来解决耦合电子核运动的计算机模拟将用于预测和解释实验。我们将研究小型、孤立的分子系统的动力学和控制这个建议。尽管如此，我们通过这项研究学到的东西很可能适用于许多其他具有超快化学动力学的光吸收系统的量子尺度操纵。因此，这项工作与广泛的纳米级系统相关：纳米颗粒、催化复合物、生物分子、有机光电子学、二维材料和其他先进材料。我们正在研究的超快量子科学不仅为分子的基本行为提供了新的见解，还可能带来未来的量子设备，其中量子系统内的电荷、能量和信息的流动可以通过超快光场来控制。