Complex Chemistry and Chemical Activation

复杂化学过程的模型，如燃烧或大气化学，假设参与的分子是热化的，也就是说，它们的能量是由系统的温度表征的。化学活化（CA）发生时，反应释放的能量被引导到产物，它们的能量比热预测的要大。这些活性物质的反应性与热化物质相比如何？CA的意义是什么？如何将CA纳入复杂系统的化学模型？这些是我们项目的核心问题：复杂化学和化学活化（C3A）。CA的各个方面已经被了解了100多年，事实上，2022年标志着林德曼机制（Lindemann Mechanism）诞辰100周年，这是第一个解释某些化学反应的压力依赖性的理论。CA的模型已经变得越来越复杂，但关键过程（能量传递，状态密度的计算）的不确定性限制了这些系统的动力学和热力学预测的准确性。通过新的实验数据和基础模型的发展来解决当前模型这些方面的不确定性是C3A的一部分。最近，这个小组和其他地方的工作表明，那些被认为可以通过热化试剂充分模拟的系统，如抽象反应（如OH + HCHO），确实需要在化学活化的背景下考虑。在2018年的一篇综述中，Klippenstein指出：“这些研究最终使我们认识到，在燃烧温度下，反应前热化的基本假设并不总是有效的，而且它的分解会显著影响关键的燃烧特性”（Proceedings of the combustion Institute, 36, p77）。这些现象并不局限于燃烧；等离子体化学和地球及其他行星的大气化学提供了其他重要的应用实例。C3A是利兹大学和牛津大学的领导小组之间的合作，他们都对实验和理论感兴趣。C3A将产生丰富的新实验数据，结合理论解释，将使我们能够评估CA在实际系统中的重要性，并提供工具，使CA能够准确地纳入这些过程的化学模型。C3A对工业的影响将通过与壳牌、达索系统和AirLabs的合作来促进。这些模型是理解重要问题的重要工具，从当前高度实际的问题（如何优化燃烧系统以最大限度地减少二氧化碳排放并改善空气质量）到未来的问题（航空生物燃料，可再生能源储存的新方法，如氨的产生和燃烧），再到重要的基本问题，如模拟热木星系外行星或星际介质的大气。准确评估并将CA纳入此类模型将显著提高模型的可靠性和预测价值。

Models of complex chemical processes such as combustion or atmospheric chemistry assume that the molecules taking part are thermalized, that is that their energy is characterized by the temperature of the system. Chemical activation (CA) occurs when the energy released by a reaction is channelled into the products and they have an energy greater than would be thermally predicted. How does the reactivity of these activated species compare with their thermalized equivalents? What is the significance of CA? How can CA be incorporated into chemical models of complex systems? These are the questions at the heart of our project: Complex Chemistry and Chemical Activation (C3A).Aspects of CA have been known about for more than 100 years, indeed 2022 marks the centenary of the Lindemann Mechanism, the first theory proposed to explain the pressure dependence of some chemical reactions. Models of CA have grown in sophistication, yet uncertainties in key processes (energy transfer, calculation of densities of states) limit the accuracy of kinetic and thermodynamic predictions from such systems. Addressing the uncertainties in these aspects of current models through new experimental data and developments in fundamental models is one strand of C3A.More recently, work in this group and elsewhere has shown that systems which were thought to be adequately modelled by thermalized reagents, such as abstraction reactions (e.g. OH + HCHO), do need to considered in the context of chemical activation. In a 2018 review, Klippenstein states: 'These studies ultimately led us to the realization that at combustion temperatures, the foundational assumption of thermalization prior to reaction is not always valid, and further that its breakdown significantly affects key combustion properties' (Proceedings of the Combustion Institute, 36, p77). These phenomena are not limited to combustion; plasma chemistry and the atmospheric chemistry of Earth and other planets provide other important examples of applications.C3A is a collaboration between leading groups from Leeds and Oxford, both with interests in experiments and theory. C3A will generate a wealth of new experimental data, which in combination with theoretical interpretation, will allow us to assess the significance of CA in real systems and provide the tools to allow CA to be accurately incorporated into chemical models of of these processes. The impact of C3A to industry will be facilitated by collaborations with Shell, Dassault Systemes and AirLabs.Such models are essential tools for understanding important questions from current highly practical issues (how can combustion systems be optimized to minimize CO2 emissions and improve air quality) to future questions (biofuels for aviation, novel methods of renewable energy storage such as ammonia generation and combustion) to important, fundamental questions such as modelling the atmospheres of hot-Jupiter exo-planets or the interstellar medium. The accurate assessment and incorporation of CA into such models will significantly enhance their reliability and predictive value.