Imaging Chemical Dynamics with Ultrafast Laser Spectroscopy

这个程序揭示了分子是如何在飞秒时间尺度上变化的，它的动机是化学功能取决于形式的原则。在化学反应过程中观察结构动力学揭示了可以推断分子行为或用于合成新药物和催化剂的信息。这种测量通常使用光谱学，根据分子吸收不同频率的光来表征分子。随着时间的推移，这些“指纹”光谱被观察到，以跟踪反应。然而，分子并不一定能吸收容易接近的频率的光，这意味着重要的化学反应往往是光谱黑暗的。物理学中一项新技术——库仑爆炸成像技术的出现，为直接研究这种暗化学提供了令人兴奋的可能性。这种方法使用强烈的超快激光脉冲（35秒）从分子中快速移除结合电子，留下许多带正电的位点，根据库仑定律爆炸成碎片。测量这些碎片的相对速度并将其与时间的函数联系起来，可以在反应的不同阶段重建爆炸前分子的形状。本研究将启动光化学反应，并利用库仑爆炸成像技术探测其结构变化。它的主要目标将是观察完整的反应，特别是当它们通过短寿命结构时，包括中间体和过渡态，这对控制分子的反应性和计算预测这种行为具有重要意义。这个项目也将是第一个直接成像光谱暗生物光化学，并可能揭示重要反应的信息，如DNA在紫外线下的稳定性。揭示这种未知的化学将使我们能够更好地控制这些机制，从而在生命和物理科学中产生新的光驱动化学或设备。上述里程碑将通过三个项目实现。第一个项目将在牛津大学开发库仑爆炸成像实验，用于分析通过电喷雾电离分离的生物分子。这将创造一种独特的途径来成像结构生物学，而不需要晶体学，这将被用作研究生物分子动力学的起点。这些问题将通过其余两个项目进行调查。其中一人将在牛津大学开发一种专用的台式仪器，利用时间分辨库仑爆炸成像技术记录基础化学的“分子电影”。最终项目将在德国电子同步加速器（DESY）上使用FLASH自由电子激光器进行，该激光器允许分子结构选择性电离。我的团队将与DESY的研究人员合作，利用这种选择性研究核碱基和芳香氨基酸中的电荷传输，揭示对其基本化学的新见解。

This programme reveals how molecules change on the femtosecond timescale and is motivated by the principle that chemical function depends on form. Observing structural dynamics during chemical reactions reveals information that can infer molecular behaviour or be used to synthesise new pharmaceuticals and catalysts. Such measurements conventionally use spectroscopy, which characterizes molecules according to the light they absorb at different frequencies. These 'fingerprint' spectra are observed over time to follow a reaction. However, molecules do not necessarily absorb light at easily accessible frequencies, meaning that important chemistry is often spectroscopically dark.The emergence of a new technique in physics, Coulomb explosion imaging, opens the exciting possibility of investigating this dark chemistry directly. This method uses an intense and ultrafast laser pulse (35 fs) to quickly remove binding electrons from a molecule, leaving many positively charged sites that explode into fragments due to Coulomb's law. Measuring and correlating the relative velocities of these fragments as a function of time allows the shape of the molecule before the explosion to be reconstructed at different stages of a reaction. This research will initiate photochemical reactions and probe their structural changes using Coulomb explosion imaging. Its key aim will be to observe complete reactions, particularly as they pass through short-lived structures, including intermediates and transition states that are of fundamental importance to controlling the reactivity of a molecule, and for predicting such behaviour computationally. This programme will also be the first to directly image spectroscopically dark biological photochemistry, and could reveal information on vital reactions, such as the stability of DNA with respect to UV light. Revealing this unknown chemistry will enable greater control of these mechanisms, leading to new light-driven chemistry or devices in the life and physical sciences.The milestones outlined above will be reached through three projects. The first will develop a Coulomb explosion imaging experiment at the University of Oxford for the analysis of biomolecules isolated through electrospray ionisation. This will create a unique pathway to image structural biology that does not require crystallography, and which will be used as a starting point for investigating biomolecular dynamics. These will be investigated through the remaining two projects. One will develop a purpose-built tabletop instrument at Oxford to record 'molecular movies' of fundamental chemistry using time-resolved Coulomb explosion imaging. The final project will be undertaken using the FLASH free electron laser at the Deutsches Elektronen Synchrotron (DESY), which allows molecular structures to be site-selectively ionised. My group will collaborate with researchers at DESY to use this selectivity to study charge transport in nucleobases and aromatic amino acids, revealing new insights into their essential chemistry.