Structure determination of unstable species by gas electron diffraction

分子结构通常被简单地理解为原子如何结合成分子。然而，虽然分子A-B-C将具有与A-C-B完全不同的性质，但重要的是要认识到，大小和形状（距离和角度）在决定分子具有的化学和物理性质方面也至关重要。较大的分子也可以采用一种以上具有相同连通性的不同形状（构象）。分子的几何结构可以在固相、液相和气相中进行研究。我的专业领域是使用气体电子衍射（GED）来确定气相结构。在气相中，分子不受相邻分子的影响，而这在固态中是很重要的。这就是为什么GED是一种非常重要的结构技术，可以帮助化学家了解分子在不同相中的行为。当科学家为分子的结构和功能建模时，他们的计算机程序使用基于实验气体结构的标准参数（距离、角度和二面角）。因此，总是需要从气相实验中获得新的结构信息，以保持这些程序的最新状态，并为科学家提供最好的预测工具，以帮助他们的工作。虽然有很多稳定分子的气体结构信息，即那些以其首选连接和构象存在很长时间的分子，但关于短寿命或不稳定物种的信息是有限的。如果要模拟反应途径，这些数据是很重要的。中间体的寿命非常短，因此在使用计算机模拟反应时，关于它们结构的准确信息将是必不可少的。该项目的目的是提供有关气相中短寿命和不稳定物种的结构信息。这将通过发展新技术和实验来实现。爱丁堡GED设备将进行修改，以适应研究不稳定样品所需的新入口系统，这些样品必须在原位生成。将开发方法和设备来研究需要在非常高的温度下处理的分子结构，这在英国目前还无法完成。在这项工作中，将研究不稳定的分子，其寿命在微秒范围内。就其性质而言，它们需要在原位生成，要么通过与入口管内的化学物质反应，要么通过加热。

Molecular structure is often simply perceived as how atoms join together in molecules. However, while molecule A-B-C will have properties totally different from those of A-C-B, it is important to realise that the size and shape (distances and angles) are also critically important in determining the chemical and physical properties the molecule possesses. Larger molecules can also adopt more than one different shape (conformation) with the same connectivity. The geometric structures of molecules can be studied in the solid, liquid and gas phases. My area of expertise is the use of gas electron diffraction (GED) to determine vapour-phase structures. In the gas phase, molecules are free from the effects of neighbouring molecules that are significant in the solid state. This is why GED is a very important structural technique to help chemists understand the behaviour of molecules in different phases. When scientists model the structures and functions of molecules, their computer programs use standard parameters (distances, angles and dihedral angles) that are based on experimental gaseous structures. New structural information from gas-phase experiments is therefore always required to keep these programs up-to-date and to provide scientists with the best predictive tools possible to aid their work. Whilst there is a lot of gaseous structural information for stable molecules, i.e. those that exist in their preferred connectivity and conformation for a very long time, the information about short-lived or unstable species is limited. Such data are important if reaction pathways are being modelled. Intermediates are very short-lived, and accurate information about their structures will be essential when using computers to simulate reactions. The aim of this project is to provide structural information about short-lived and unstable species in the gas phase. This will be achieved by developing new techniques and experiments. The Edinburgh GED apparatus will be modified to accommodate the new inlet systems required to study the unstable samples, which have to be generated in situ. Methods and equipment will be developed to study the structures of molecules that require handling at very high temperatures, which at present cannot be done in the UK. In this work, molecules will be studied that are unstable, with lifetimes in the microsecond range. By their nature they need to be generated in situ, either by reaction with a chemical in the inlet tube or by heating.