氟/氯原子加甲烷分子及其同位素取代反应的态-态量子动力学研究

The reaction of halogen atom with methane is of great importance in both atmospheric and combustion chemistry. Similar to the F+H2/HCl/H2O reaction, the F+CH4 reaction has an inverted HF product vibrational state distribution, which can be used as the new HF chemical laser system. Theoretically, it is still a great challenge to study a six-atom reaction. Up to now, all the dynamical quantities were calculated by using QCT method or limited to total reactive cross sections, which were not able to compete in accuracy with state-of-the-art experiments. In this project, full-dimensional global PES for the ground electronic state of F/Cl+CH4 will be constructed using the neural networks method. The project is also aimed to develop and apply the state-to-state quantum dynamics theories and programs with seven/eight degrees of freedom to study the X+YCZ3→XY+CZ3 type reaction. We will calculate differential cross sections for F/Cl+CH4/CHD3 reaction from the ground and some vibrationally excited initial states. We will investigate reaction resonance phenomenon in the process and the effect of reagent vibrational excitation on a state-to-state level. With the cooperation of high-resolution, crossed-molecular beam experiment, the successful accomplishment of the project will not only push forward the development of polyatomic reaction dynamics field, but also provide theoretical foundations for developing new chemical laser systems.

研究卤素原子与甲烷的反应对大气和燃烧化学有着重要的意义。而F+CH4和F+H2/HCl/H2O反应一样，得到的产物HF也有振动态布居反转，可以作为新的化学激光体系。理论方面，六原子反应体系的研究仍然是一个巨大的挑战。目前对F/Cl+CH4反应的动力学计算大多使用准经典轨线方法或局限在反应总截面，缺少能在量子态分辨层次上与实验直接比较的精确理论结果。本项目中，我们将运用神经网络方法构建F/Cl+CH4反应新的电子基态全维全域势能面，并发展X+YCZ3→XY+CZ3反应类型的7-8维态-态量子动力学方法与程序。我们将计算F/Cl+CH4/CHD3初始基态和部分振动激发态反应的微分截面，研究反应过程中是否存在共振态现象及其机理，研究CH4分子振动激发对产物末态分布的影响。这些工作与高分辨的交叉分子束实验结果结合，将推动多原子反应动力学的发展，还将为基于新反应途径的化学激光体系提供理论基础。

在项目执行期间，我们按研究计划运用神经网络方法构建了F+H2O，Cl+CH4和F+CH4反应目前为止最精确的电子基态全维全域势能面；基于含时波包方法发展完善了一套有效的八维态-态量子动力学方法和程序，首次实现了包含甲烷六原子反应微分截面的目前最为精确计算，结合交叉分子束实验在Cl+CH4反应中发现了重-轻-重反应几率振荡现象；还对F+H2O/CH4及其同位素取代反应进行了量子态-态计算，在F+H2O反应中发现了由产物分子间偶极相互作用所产生的共振，在F+HOD(vOH/vOD=1)反应中发现了化学键软化导致的共振，把对Feshbach共振的理解从三原子反应扩展到多原子反应；此外我们把含时波包计算扩展到超冷四原子反应散射，计算了OH+H2(v=2,j=0)→H2O+H反应Bethe-Wigner阈值区域以上的精确积分截面和速率常数；还研究了H+Br2、H2+HS、H+CO2等一系列重要的三原子和四原子反应。项目的成功实施推动了多原子反应动力学的发展。资助期间，共发表SCI文章10篇，包括1篇Nature Communications，1篇PNAS，2篇Journal of Physical Chemistry Letters。