光致锥形交叉的形成机理及影响因素的研究

With a strong femtosecond laser, molecular potential surfaces can be dynamically modified, and light-induced conical intersection (LICI) can be created, leading to completely different quantum state evolution and results. Creation and modulation of LICI has a very beautiful picture in application prospect, it can be used for quantum control of chemical reaction, and also helpful for optimize and design the molecular devices. However, the study correlated with LICI just started, the research exists almost limited to the theoretical calculation and simulation. The physical mechanism about how LICI is created, and what condition LICI depends is not clear. In order to answer these questions, we carry out our research from the view of molecular photodissociation dynamics. Start with simple polyatomic molecule of NH3, LICI is prepared on the path where the molecular dissociation wavepacket moves by using a strong femtoscond laser, we will investigate how the LICI influence the dissociation channels, the quantum yields of dissociation products and also the kinetic energy distributions. By changing the intensity, frequency, pulse width, polarization of the strong femtosecond laser and so on, we will investigate how LICI changes and reacts to these different conditions. With the help of the theoretical calculation and simulation, we will uncover the physical mechanism of how LICI is created, and how the nonadiabatic coupling influences the evolution of molecular quantum states. This research will help us to find new schemes for quantum controlling of chemical reactions and design of molecular devices.

在飞秒强光场作用下，分子势能面可能会发生改变，形成光致锥形交叉，导致完全不同的分子激发态演化过程及结果。制备和调控光致锥形交叉有着很广阔的应用前景，既可以实现对化学反应的控制，又可能实现对分子器件性能的优化和设计。目前有关光致锥形交叉的研究仍处于起步阶段，相关研究也主要限于理论计算和模拟，其形成的物理机理及影响因素并不十分清楚。基于此科学问题，本项目拟选择分子光解反应作为载体开展相关研究。研究计划从简单的多原子分子NH3着手，利用飞秒激光产生的强场效应在分子解离波包运动路径上制备光致锥形交叉，研究其对解离通道、解离产物的量子产率及动能分布的影响。从强度、频率、啁啾、偏振等方面阐明不同光场条件对光致锥形交叉的形成及结构的影响。结合理论模拟，揭示光致锥形交叉产生的物理机理以及非绝热耦合作用对分子激发态演化产生的影响。该工作的开展有助于为控制化学反应、设计和优化分子器件等提供新思路。

飞秒强光场的作用会使分子势能面发生改变，导致锥形交叉处态态之间的相互作用发生强烈变化，通过制备和调控锥形交叉可以达到控制化学反应的目的。本项目选择分子光解反应作为载体开展相关研究。将飞秒泵浦-探测技术与离子速度影像技术相结合，开展多原子分子在无场条件下的光解动力学研究。揭示分子激发态势能面锥形交叉处，激发态-激发态之间的非绝热耦合相互作用对分子波包演化产生的作用和影响。对分子波包的演化进行跟踪，对解离产物及产率进行探测。结合理论计算，揭示分子波包的演化路径及动力学过程。在无场研究的基础上，利用飞秒泵浦-控制-探测技术，进一步开展有场条件下的光解动力学调控研究。我们选择合适波长的飞秒激光，利用其产生的强场效应，对分子势能面进行微扰和调控，尤其是对于锥形交叉进行制备和调控。与无场条件下的测量结果相比较，研究光致锥形交叉的制备和调控对光解产物及通道的影响。进一步，开展不同光场条件下，如改变控制光场的强度、频率、偏振等，研究有场条件下分子光解动力学的变化，包括解离路径，解离产物以及产率等，分析和总结控制光场的各项参数对于锥形交叉的行成、位置和结构之间的关系，深入剖析光致锥形交叉的机理和影响。目前，我们已经成功实现了对简单三原子分子OCS，以及复杂多原子分子碘苯、间氟苯酚等分子光解反应通道及产物的控制。研究发表论文12篇，均标注课题基金号。