为了探究大气中羟基自由基的来源及反应机理，本课题探究了O3-H2O超分子和H2O分子光解离过程。在CASPT2//CASSCF/cc-PVDZ计算水平上利用内禀反应坐标理论(IRC)和从头计算动力学模拟(AIMD)的方法在分别计算了O3-H2O超分子与H2O分子的最小能量路径(MEPs)和动力学轨迹。基态O3-H2O超分子在吸收248nm的光后，电子跃迁到SPP(,1ππ*)激发态，随后在SPP(,1ππ*)态上的O2-O3键迅速断裂并产生了高能态O(1D)原子，这一超快过程的时间尺度为飞秒级。高能态O(1D)原子向H2O分子迁移靠近，迫使H2O分子中H6-O4键断裂，发生氢抽取反应，这一无垒过程最终导致O2(a1∆g)+OH(2Π)+OH(2Σ)产物的生成。激发态动力学模拟发现，羟基自由基的形成对O3和H2O分子之间的空间取向非常敏感，只有少量特定构型的O3-H2O超分子才能发生抽氢反应。Stable trans式与其它6种O3-H2O(1:1)超分子异构体共存，并且在复合物中占有的比例很小，计算表明只有70%的stable trans式构型在SPP(,1ππ*)可以生成羟基自由基。即便其动力学显示形成OH自由基是一个超快无垒过程，O3-H2O超分子生成OH自由基的量子产率也要比之前预测低得多。H2O分子光解过程十分复杂，我们研究了态和态的光激发过程，电子态能直接快速解离生成H原子和OH基态产物,电子态既可以通过直接解离生成H原子和OH激发态产物，也可以通过与态和态的非绝热耦合间接解离生成H原子和OH基态产物,且后者解离方式占主导地位。

The intrinsic reaction coordinate computations and ab initio molecular dynamic simulations at CASPT2//CASSCF/cc-PVDZ level of theory were used to deeply understand the photo-dissociation dynamics of O3-H2O complex and H2O monomer in excited state and its atmospheric implications. The ground state O3-H2O complex is promoted to populate in the highly excited SPP(,1ππ*) state by ~248 nm photo-excitation, which is mainly responsible for maximum absorption of ozone in stratosphere. This rapidly initiates the occurrence of the O−O bond fission in the SPP(,1ππ*) state, producing the high energy of O(1D) within femtosecond timescale. The approaching of O(1D) and water molecule causes the broken of H-O bond in H2O to give rise to O2(a1∆g)+OH(2Π)+OH(2Σ) products along a downhill pathway. The excited state dynamic simulations conclude that the formation of hydroxyl radical is very sensitive to the spatial orientation between ozone and water molecules. The stable trans isomer is determined to possess a small portion in seven coexistent O3-H2O complex conformers, 70% of which is the unique source to produce OH radicals in SPP(,1ππ*) state. As a result, the quantum yield of atmospheric hydroxyl radical through the ozone-water complex photolysis is much lower than the previous expectation. H2O molecule photolysis process is very complex, we studied the optical excitation process of and state. electronic state can directly and rapidly dissociate to produce H atom and OH-state products. electronic state can either through direct dissociation to produce H atom and OH excited state products or can also be coupled with the state and the state of non-adiabatic dissociation indirectly generate H atoms and OH-state product, the latter mode was the dominant dissociation way.