Time-resolved Velocity Map Imaging using Pixel Imaging Mass Spectrometry

该项目将专注于atto-纳秒系统的时间分辨离子成像，属于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中能量的基本分配，以及在单个实验中不同离子的相关信息，可以在很短的时间尺度内收集有关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比碎片的全三维速度分布。因此，在我的项目中，将进行几种带有VMI成像的PImMS相机的应用。纳秒时间分辨成像将在牛津进行，使用泵-探针方案光解分子氯。后续氯原子的PEDA （post - extraction differential acceleration）切片成像技术是一种提高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。这样就得到了氯原子的三维图像，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FLASH研究飞秒时间尺度上的系统。这些实验将使用PImMS传感器进行一系列实验，利用时间分辨成像技术来制作“分子电影”：通过光激发改变分子的结构，并将产生的图像记录在飞秒时间尺度上，从而制作出结构变化和随后动力学的有效视频。飞秒时间分辨成像也将与奥胡斯的Henrik Stapelfeldt教授合作进行；扩展了以前使用PImMS传感器的工作。这项工作是建立在飞秒激光诱导库仑爆炸后研究异构体和识别苯衍生物的基础上的，其最终目标是使用超短时间尺度区分手性分子。使用PImMS传感器，不同质量的离子可以通过协方差图相互关联，这意味着人们可以看到特定离子相对于参考离子撞击探测器的位置。由此得出的推论是，样本的特定结构可以通过一些协方差图推断出来。利用阿秒时间分辨成像与伯克利合作是另一种可能性探索。这与电子动力学相对应，可以在电荷再分配过程中对电子进行成像，从而对这个超快速、鲜为人知的过程的动力学获得前所未有的了解。了解电子如何重组对许多新兴领域如分子电子学具有重要意义。

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.