Time-resolved Velocity Map Imaging using Pixel Imaging Mass Spectrometry

本计画将著重于时间分辨的离子成像，在阿托至纳秒系统和福尔斯内的EPSRC物理科学研究领域。速度图成像（VMI）通过提供散射光碎片的直接图像，彻底改变了光解动力学领域。这些揭示了光化学反应过程中能量的基本分配，并且在单个实验期间不同离子的这种信息的相关性允许在非常短的时间尺度上收集关于反应机制和结构变化的信息。将VMI与像素成像质谱（PImMS）时间戳传感器相结合，可以直接记录多个质荷碎片的完整三维速度分布。因此，在我的项目中，将进行几个应用的PImMS相机与VMI成像。纳秒时间分辨成像将在牛津大学使用泵浦-探测计划，以光解分子氯。后续原子氯的PEDA（提取后差分加速）切片成像是一种增强飞行时间分辨率的技术，结合具有多质量成像和时间戳能力的PImMS传感器的应用，可以获得一系列图像。因此，获得了氯原子的3D图像，并确定了角动量极化率。该项目将在汉堡的一个同步加速器设施中使用自由电子激光器FLASH研究飞秒时间尺度上的系统。这些将使用PImMS传感器进行一系列实验，采用时间分辨成像来创建“分子电影”：其中分子的结构通过光激发改变，并且在飞秒时间尺度上记录所得图像，以创建结构变化和后续动态的有效视频。飞秒时间分辨成像也将与奥胡斯的Henrik Stapelfeldt教授合作进行;使用PImMS传感器扩展以前的工作。这项工作是建立在研究异构体和确定苯衍生物的飞秒激光诱导库仑爆炸后，使用超短时间尺度区分手性分子的最终目标。不同质量的离子可以使用PImMS传感器通过协方差图相互关联，这意味着可以看到特定离子相对于参考离子撞击检测器的位置。由此推断，样本的特定结构可以通过许多协方差图推断出来。与伯克利合作利用阿秒时间分辨成像是另一种有待探索的可能性。这对应于电子动力学，并将允许在电荷重新分布期间对电子进行成像，从而对这种超快，鲜为人知的过程的动力学获得前所未有的洞察力。了解电子如何重组对许多新兴领域（如分子电子学）至关重要。

This project will focus on time-resolved ion imaging at the atto- to nanosecond systems and falls within the EPSRC Physical Sciences research area. Velocity map imaging (VMI) has revolutionised the field of photodissociation dynamics by providing direct images of scattered photofragments. These reveal the fundamental partitioning of energy during photochemical reactions, and correlation of such information for different ions during a single experiment allows information to be gleaned about reaction mechanisms and structural changes over very short timescales. Coupling VMI with the Pixel Imaging Mass Spectrometry (PImMS) time-stamping sensor allows the full three-dimensional velocity distribution of multiple mass-to-charge fragments to be directly recorded. As a result, several applications of the PImMS camera with VMI imaging will be carried out during my project.Nanosecond time resolved imaging will be conducted in Oxford using a pump-probe scheme to photodissociate molecular chlorine. PEDA (post extraction differential acceleration) slice imaging of the subsequent atomic chlorine is a technique that enhances the time of flight resolution, which in conjunction with the application of the PImMS sensor with multi-mass imaging and time stamping capabilities, can obtain a series of images. A 3D image of the atomic chlorine is thus obtained and angular momentum polarisabilities determined. The project will look to study systems on a femtosecond timescale using the free-electron laser FLASH at a synchrotron facility in Hamburg. These will use the PImMS sensor to undergo a series of experiments employing the use of time resolved imaging to create a "molecular movie": where a molecule's structure is altered via photoexcitation and the resulting images recorded on a femtosecond timescale to create an effective video of the structural change and subsequent dynamics. Femtosecond time-resolved imaging will also be undertaken in collaboration with Professor Henrik Stapelfeldt in Aarhus; expanding on previous work using the PImMS sensor. This work is built upon studying isomers and identifying benzene derivatives following a femtosecond laser-induced Coulomb explosion, with an ultimate goal of distinguishing chiral molecules using an ultra-short timescale. Ions of different mass can be correlated to one another using the PImMS sensor through covariance maps, meaning that one can see where a particular ion hits the detector relative to a reference ion. The inference of this is that the particular structure of the sample can be deduced through a number of these covariance maps. The utilisation of attosecond time- resolved imaging in collaboration with Berkeley is another possibility to be explored. This corresponds to electronic dynamics and would allow imaging of electrons during charge redistribution, gaining unprecedented insight into the dynamics of this ultra-fast, little understood process. Understanding of how electrons reorganise is of fundamental importance to many emerging fields such as molecular electronics.