Portable femtosecond pump-probe facility (PORTO) for dynamic structural science

近100年来，用X射线衍射法确定分子或固体中的原子排列已经是可行的；大多数关于盐、胰岛素、血红蛋白以及足病和鼠疫病毒结构的“图片(剧照)”都是基于这种从晶体中散射X射线的技术。对于有序度较低的材料，如玻璃和液体溶液，可以从X射线吸收光谱中得出局部局部结构。这两种技术都需要散射电子，从而告诉我们原子的排列和对电子分布的一些洞察。化学和光诱导的变化是电子和原子到新位置的运动，因此用X射线方法可视化这些演化可以提供反应的化学视频，这些反应比静止照片前后更丰富；这就是描绘奔驰的马的分子平行。原子运动的时间尺度通常在1/100到1皮秒(1ps=百万分之一微秒)之间发生变化，这已经通过紫外光和可见光光谱(颜色)的变化进行了监测。这几乎没有提供关于结构的信息。红外光谱可以用于大于1ps的时间尺度，并且是分子中官能团的特征。这一提议提供了一种通过化学变化来接近分子“静止”细节的方法。钻石光源是英国最明亮的X射线光源，它提供了在10皮秒的时间尺度上研究结构的机会。这足以捕捉到荧光材料的许多激发态，并观察到最活跃的瞬时分子的反应。在大约1/5皮秒的激光脉冲引起变化后，将对紫外-可见和红外光谱进行监测。快速激光光谱学将与迅速发展的光结晶学技术相结合，有可能获得寿命在纳秒到毫秒范围内的光激活物种的全三维固态结构，从而有可能制作展示关键化学和生物过程如何发生的“分子电影”。因此，有可能研究从皮秒到毫秒的时间尺度上的重要催化、传感器和非线性材料，以了解性质和功能如何随着时间的推移而发展。将制定晶体、溶液和薄膜的取样程序，并向其他研究小组提供。整个方法应该改变我们思考化学反应的方式。从这样的方法中，将会有一小部分问题，对于这些问题，甚至更快的测量将是令人着迷的。近年来，美国和日本(通过X射线自由电子激光，XFELs)已经可以获得X射线区域的激光，欧洲(德国和瑞士)正在建造光源。它们提供大约1/50皮秒的X射线脉冲，比大多数分子振动更快，因此化学反应的X射线电影是可行的。这一提议将为化学科学的研究人员提供一个试验台，以开发他们的技术来可视化他们的反应。该设施将设在哈韦尔基地，毗邻钻石光源和中央激光设施的设备和专业知识，这两个设施都是最高级别的用户设施。

Establishing the atomic arrangements in a molecule or a solid has been feasible for about 100 years by X-ray diffraction; most "pictures (stills)" of the structure of, for example, salt, insulin, haemoglobin and foot and mouse disease virus are based on this technique of scattering X-ray from crystals. For less ordered materials, like glasses and liquid solutions, partial, local structures can be derived from X-ray absorption spectroscopy. Both techniques require scattering off electrons and thus tell us about the atomic arrangements and some insight into electronic distributions.Chemical and light-induced changes are movements of electrons and atoms to new sites and so visualizing these evolutions by X-ray methods can provide chemical videos of reactions which have greater richness than before and after stills; this is the molecular parallel of picturing a galloping horse.Generally changes on the timescales of atomic motion occur between a 1/100 and 1 picosecond (1 ps = 1 millionth of a microsecond), and this has been monitored by changes in the uv and visible spectrum (colour). This provides little information about structure. Infra-red spectroscopy can be used for timescales greater than 1 ps, and is characteristic of functional groups within molecules. This proposal provides a means of approaching the detail of a molecular "still" through chemical changes. The Diamond Light Source is the brightest X-ray source in the UK, and provides the opportunity of studying structures on a timescale of 10s of picoseconds. This is fast enough to catch many excited states of fluorescent materials, and to observe the reactions of the most reactive of transient molecules. UV-visible and infrared spectroscopies will be monitored after changes induced by a laser pulse of about 1/5 of a picosecond. The fast laser spectroscopy will be combined with the rapidly developing technique of photocrystallography, where it is possible to obtain full 3-D solid-state structures of photoactivated species that have lifetimes in the nanosecond to millisecond range, so that it will be possible to make "molecular movies" showing how key chemical and biological processes occur. Thus, it will be possible to study important catalytic, sensor and non-linear materials across the time scales from picoseconds to milliseconds, to see how properties and functions develop over time. Sampling procedures for crystals, solutions and films will be developed and made available to other research groups. The whole approach should transform the way we think about chemical reactions.From such an approach there will be a fraction of problems for which even faster measurements would be fascinating. In recent years laser light in the X-ray region has become available in the USA and Japan (by X-ray free electron lasers, XFELs), and sources are being built in Europe (Germany and Switzerland). They provide an X-ray pulse of about 1/50 of a picosecond, faster than most molecular vibrations, and thus the X-ray movie of a chemical reaction is feasible.This proposal will provide a test-bed for researchers in the chemical sciences to develop their technique for visualizing their reactions. The facility will be based on the Harwell site adjacent to the equipment and expertise of the Diamond Light Source and Central Laser Facility, both of which are user facilities of the highest rank.