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

通过X射线衍射建立分子或固体中的原子排列已经可行了大约100年;例如，盐，胰岛素，血红蛋白和足鼠病病毒的结构的大多数“照片（剧照）”都是基于这种从晶体散射X射线的技术。对于不太有序的材料，如玻璃和液体溶液，部分的局部结构可以从X射线吸收光谱中得到。这两种技术都需要散射电子，从而告诉我们原子的排列和电子分布的一些见解。化学和光诱导的变化是电子和原子向新位置的运动，因此通过X射线方法可视化这些演变可以提供比静止前后更丰富的化学反应视频;这是一个与描绘一匹疾驰的马的分子平行的现象。通常，原子运动的时间尺度的变化发生在1/100到1皮秒之间（1 ps =百万分之一微秒），这已经通过紫外和可见光谱（颜色）的变化来监测。这提供了关于结构的很少信息。红光光谱可用于大于1 ps的时间尺度，并且是分子内官能团的特征。这一提议提供了一种通过化学变化接近分子"静止"细节的方法。钻石光源是英国最亮的X射线源，提供了在10皮秒的时间尺度上研究结构的机会。这是足够快，以捕捉荧光材料的许多激发态，并观察最活跃的瞬态分子的反应。紫外-可见和红外光谱将在约1/5皮秒的激光脉冲引起的变化后进行监测。快速激光光谱学将与快速发展的光晶体学技术相结合，可以获得寿命在纳秒至毫秒范围内的光活化物质的完整三维固态结构，从而可以制作“分子电影”，展示关键的化学和生物过程如何发生。因此，将有可能在从皮秒到毫秒的时间尺度上研究重要的催化，传感器和非线性材料，以了解性能和功能如何随时间发展。将制定晶体、溶液和薄膜的取样程序，并提供给其他研究小组。整个方法应该会改变我们对化学反应的思考方式，从这样的方法中，会有一小部分问题，甚至更快的测量也会很吸引人。近年来，美国和日本（通过X射线自由电子激光器，XFEL）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。它们提供的X射线脉冲约为1/50皮秒，比大多数分子振动都快，因此，化学反应的X射线电影是可行的。这项提议将为化学科学研究人员提供一个试验平台，以开发可视化反应的技术。该设施将设在Harwell场址，毗邻钻石光源和中央激光设施的设备和专门知识，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.