电子动量谱学是一种独特的研究原子分子电子结构的实验手段，可以获得分子轨道动量空间的电子密度分布。受谱仪效率的限制，该技术多应用于气相原子分子基态电子态的研究，而物理和化学上感兴趣的低密度靶体系，如激发态分子、取向分子等，传统谱仪的灵敏度则远远不够，更无法实现时间分辨的电子动量谱学测量。本项目拟在项目组最新发展的高灵敏第四代电子动量谱学技术的基础上，研制时间分辨的电子动量谱仪，其基本思想是利用一束泵浦激光选择性地将分子激发到特定的电子激发态，即制备初始波包。利用可调延时的快脉冲电子束使激发态分子体系电离，测量不同pump-probe 时间延时的电子动量分布，从而“拍摄”波包演化过程中电子云变化的影像。项目拟初步实现30-50 ns 的时间分辨。谱仪一旦研制成功将成为分子动力学研究的有力工具。

Electron momentum spectroscopy (EMS) has shown to be a powerful tool for investigating the electronic structure of atoms and molecules by measuing the electron density distributions in momentum space for individual orbitals. However, limited by the low coincidence count rate, most of the EMS applications are restricted to the valence orbitals of atoms and relatively small and stable molecules, while low density targets of chemical interests, such as radicals and oriented molecules, are beyond the ability of conventional EMS instruments, to say nothing of time-resolved measurements. The project is planned to develop time-resolved electron momentum spectrometer based on the newly-devoloped high-sensitivity fourth-generation EMS. The basic idea is to prepare the initial electron wave packet by exciting molecular system selectively using a pump laser pulse. The “movie” of the evolution of the wave packet is “shot” through measuring the electron momentum distribution by ionizing the excited molecule by a fast electron probe pulse after adjustable time delay. The time resolution is supposed to be 30~50 ns. The spectrometer will be a powerful tool for the study of molecular dynamics.