Criegee中间体，即羰基氧化物，在大气中非常重要，其生成、单分子分解以及与环境物质发生的双分子反应等都在大气环境中起着重要作用。虽然已有大量的关于该中间体的研究，但对其化学性质的认识还远远不够，不同的研究之间存在差异。本项目使用计算化学方法对最简单Criegee中间体CH2OO进行全面细致的研究。采用振动自洽场/组态相关方法(VSCF/VCI)模拟CH2OO不同异构体的振动光谱，验证和指导实验。采用准经典轨线方法，研究CH2OO自身分解生成不同产物通道的模式选择性、反应分支比等，分析不同产物的能量和态分布，特别关注生成OH的机理和能态分布。采用准经典轨线方法，研究CH2OO和惰性气体Ne在不同起始态的碰撞过程。探索使用交换对称多项式结合神经网络的方法构建CH2OO和Ne的相互作用能。本项目将促使相关实验工作的开展，并为实验提供理论支持，进而深化对CH2OO和Criegee中间体的认识。

Criegee intermediates (CIs), i.e. carbonyl oxides, are important in the atmosphere, due to that the reactions involved in CIs, including their formation, uni-molecular decomposition, and bimolecular reactions with other environment species, play significant roles in the atmosphere. CIs have drawn much attention or many researchers, however, our knowledge on their chemistry is far from complete and there are still differences amongst different investigations. In this project, we outline a comprehensive and detailed research plan for the simplest Criegee intermediate CH2OO by using theoretical chemical methods. The vibrational spectroscopy of different isomers of CH2OO will be simulated by the vibrational self-consistent field/virtual configuration interaction (VSCF/VCI) approach, in order to help and validate the assignment in experiment. Furthermore, the quasi-classical trajectory approach will be employed to study the mode selectivity and branching ratio in different channels of the uni-molecular decomposition. The energy and state distributions of the products will be analyzed. Especially, the reaction mechanism to generate OH and the relevant energy/state distributions are focused. Finally, the collision process between CH2OO and the noble gas Ne will be investigated with different initial internal states. We will try to employ the permutationally invariant polynomial-neural network (PIP-NN) approach to develop the interaction between CH2OO and Ne. This project can stimulate relevant experimental investigations on CIs and provide theoretical supports for the experiments. The proposed theoretical research is expected to significantly advance our understanding of these CIs.