Exploring molecular structure and dynamics through Coulomb Explosion Imaging

分子改变形状的方式（分子动力学）可能是它们在生物系统乃至所有生命中最重要的特性。对分子形状及其如何变化或如何改变的科学探索，一直是强大工具开发背后的驱动力之一，如超短激光源（脉冲长度与分子运动的自然时间尺度相似，1飞秒的十亿分之一秒）或x射线源，如同步加速器设备，它可以激发分子改变形状，用一个高能光子。测量分子形状的一种特别吸引人的方法是库仑爆炸成像，即通过移除尽可能多的电子来使分子电离，并通过激光脉冲或x射线完全分解，然后爆炸成原子碎片。通过确定它们来自哪个方向，就有可能绘制出爆炸点分子的图像。这种方法很重要，因为它可以一次对气体中的一个分子进行成像，并绘制出精确到原子尺度（埃）的图像。折叠到成像过程中是与激光脉冲中的电离过程、分子内部运动（振动）、电离过程中启动的动力学以及所涉及的飞秒时间尺度有关的丰富的物理学。该研究项目将专注于提高图像质量，特别是在滑铁卢大学，那里的激光现在专门用于这项研究。在滑铁卢，我们将解决在大分子中使用库仑成像方法的最大障碍之一，即离子检测装置的效率。这通常只有65%，这意味着许多分子必须爆炸才能给出完整的碎片信息。一种新的探测器已经出现，它有可能达到接近100%的效率，使成像更大的生物重要分子的目标成为可能。我们将在滑铁卢测试新的探测器，目标是成像迄今为止最大的分子。该计划将使用许多方法来帮助我们理解导致分子改变形状的物理过程，其中包括使用加拿大光源的单个x射线光子电离。使用激光成像的最大动机之一是激光的可控性，这使我们能够产生特定的波长，可以在“泵”脉冲中启动动力学，随后是成像“探针”脉冲，产生库仑爆炸并创建分子的图像，通过改变两个脉冲之间的时间，我们可以记录一个“分子电影”，这将与先进的激光光源合作进一步推进。我们将尝试改进我们已经令人印象深刻的质子从乙炔分子的一端移动到另一端的视频。

The way that molecules change their shape (molecular dynamics) is perhaps their most important property at the heart of biological systems and therefore all life. The scientific quest to image molecular shape and how it changes, or can be made to change, has been one of the driving forces behind the development of powerful tools such as ultrashort laser sources (with pulses similar in length to the natural timescale of a molecular motion, one thousand million millionth of a second one femtosecond) or x-ray sources such as synchrotron facilities, which can excite a molecule to change shape with one high energy photon. A particularly appealing method for measuring molecular shape is Coulomb Explosion Imaging or CEI in which the molecule is ionized by removing as many electrons as possible and completely broken apart by either the laser pulse or the x-ray and literally explodes into atomic fragments. By determining what direction they came from, it is possible to actually make an image of he molecule at the point of explosion The method is important because it can image one molecule at a time in a gas and create an image which is accurate to the scale of atoms (Angstrom). Folded into the imaging process is a wealth of physics relating to the ionization process in the laser pulse, the molecular internal motion (vibration), dynamics initiated during ionization and the femtosecond timescales involved. The research program will focus on improving the quality of images particularly in the University of Waterloo where a laser is now dedicated to this study. In Waterloo we will tackle one of the biggest barriers to using the Coulomb imaging method with large molecules, namely the efficiency of the ion detection apparatus. This is typically only 65% which means that many molecules must be exploded before one gives complete fragmentation information. A new detector has become available which has the potential to get close to 100% efficiency, making the goal of imaging larger biologically significant molecules a possibility. We will test the new detectors in Waterloo and aim to image the largest molecules so far achieved. The program will use a number of approaches to help us understand the physical processes which lead to molecules changing shape, these will include using ionization by single Xray photons at the Canadian Light Source. One of the biggest motivations for using laser based imaging though is the controllability of lasers, which allows us to generate specific wavelengths which can initiate dynamics in a “pump” pulse followed by an imaging “probe” pulse which generates the Coulomb explosion and creates the image of the molecule, by varying the time between the two pulses we can record a “molecular movie” this will be further pursed in collaboration with the Advanced Laser Light Source, where we will attempt to improve on our already impressive movie of a proton moving from one end of an acetylene molecule to the other.