Complex Chemistry and Chemical Activation

燃烧或大气化学等复杂化学过程的模型假定参与的分子是热化的，也就是说，它们的能量由系统的温度来表征。当反应释放的能量被引导到产物中，并且它们具有比热预测更大的能量时，就发生了化学活化(CA)。这些活性物种的反应性与它们的热化等价物相比如何？CA的意义是什么？如何将CA纳入复杂体系的化学模型？这些是我们项目的核心问题：复杂的化学和化学活化(C3A)。CA的研究领域已经知道了100多年，事实上，2022年是林德曼机制的百年诞辰，这是第一个提出解释一些化学反应的压力相关性的理论。CA的模型已经发展得越来越复杂，但关键过程(能量转移、态密度的计算)中的不确定性限制了来自此类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的一条线索。最近，该小组和其他地方的工作表明，被认为可以通过热化试剂(如抽象反应(例如OH+HCHO))充分建模的体系确实需要在化学活化的背景下考虑。在2018年的一次审查中，Klippenstein指出：“这些研究最终使我们认识到，在燃烧温度下，在反应之前热化的基本假设并不总是有效的，而且它的崩溃显著影响关键的燃烧特性”(《燃烧研究所学报》，36，第77页)。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例子。C3A是来自利兹和牛津的领导小组合作的，他们都对实验和理论感兴趣。C3A将产生大量新的实验数据，这些数据与理论解释相结合，将使我们能够评估CA在真实系统中的重要性，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AirLab的合作得到促进。这些模型是理解从当前高度实用的问题(如何优化燃烧系统以将二氧化碳排放降至最低并改善空气质量)、未来问题(航空生物燃料、氨产生和燃烧等新的可再生能源存储方法)到重要的基本问题(如对热木星系外行星或星际介质的大气进行建模)的重要工具。准确评估CA并将其纳入此类模型将显著提高其可靠性和预测价值。

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.