Ling Fengzi, Wang Yanmei, Li Shuai, Wei Jie, Tang Ying, Zhang Bing
State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics , Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences , Wuhan 430071 , China.
University of Chinese Academy of Sciences , Beijing 100049 , China.
J Phys Chem Lett. 2018 Sep 20;9(18):5468-5473. doi: 10.1021/acs.jpclett.8b01841. Epub 2018 Sep 10.
Here, we demonstrate the capability of femtosecond time-resolved photoelectron imaging to visualize the reversible and irreversible structural evolution in electronically excited 2,4-difluoroaniline. As a coherent superposition of out-of-plane vibrational motions is created following 299.8 nm excitation, the molecular geometry alters periodically, thus modulating the photoionization channel. The reversible nuclear motion between distinct geometries is directly observed as the reverse beats in the time-dependent photoelectron spectra. Moreover, with the molecule highly vibrationally excited at 289.0 nm, the exponential decrease/increase changes in photoelectron signal provide a physically intuitive and complete picture of the irreversible geometry rearrangement away from a nonplanar geometry in the vertical Franck-Condon region toward the planar minimum.
在此，我们展示了飞秒时间分辨光电子成像技术可视化电子激发态2,4-二氟苯胺中可逆和不可逆结构演化的能力。在299.8nm激发后，由于产生了面外振动运动的相干叠加，分子几何结构会周期性地改变，从而调制光电离通道。在随时间变化的光电子能谱中，不同几何结构之间可逆的核运动直接表现为反向拍频。此外，当分子在289.0nm处高度振动激发时，光电子信号的指数下降/上升变化提供了一幅物理直观且完整的图像，描述了在垂直弗兰克-康登区域中，分子从非平面几何结构向平面最低能量构型进行的不可逆几何重排。
