Theoretical study on ultrafast chemical processes in terms of pump-probe photoelectron spectroscopy

我们发展了一种用于波包飞秒抽运-探测电离的能量和角度分辨光电子谱理论，并将其应用于定向Na_2的^1 Σ^+_μ双最低态。该配方是非常适合列入分子光电离的基本动力学及其对分子几何形状的依赖。结果已经获得了三个典型的泵浦激光能量选择，从而调查定性不同的模式的时空传播的波包的双最小电位曲线和它们相关的光电子谱。给出了线偏振泵浦脉冲和探测脉冲在不同取向下的光电子角分布。由此产生的光电子能谱说明了一个适当的描述的基础光电离振幅和它们的依赖几何解开波包动力学从泵探测光电子信号在非绝热区域的电子结构迅速演变的几何形状的重要性。本文的理论被推广到处理一个非绝热跃迁系统，如NaI分子，其基态和第一激发势曲线由于分子内电子转移而相互交叉。首次证明了利用泵浦-探测光电子能谱可以直接在实验上观察到原子核波包的分岔。这在化学、波速工程、量子混沌、基础量子理论等方面都具有重要意义。

We have developed a theory of energy- and angle-resolved photoelectron spectra for femtosecond pump-probe ionization of wavepackets and results of its application to the ^1Σ^+_μ double-minimum state of aligned Na_2. The formulation is well suited for inclusion of the underlying dynamics of molecular photoionization and its dependence on molecular geometry. Results have been obtained for three typical pump laser energies selected so as to investigate qualitatively different patterns of the spatio-temporal propagation of wavepackets on the double-minimum potential curve and of their associated photoelectron spectra. Photoelectron angular distributions have been given for different orientations of linearly polarized pump and probe pulses. The resulting photoelectron spectra illustrate the importance of a proper description of the underlying photoionization amplitudes and their dependence on geometry for unravelling wavepacket dynamics from pump-probe photoelectron signals in non-adiabatic regions where the electronic structure evolves rapidly with geometry. The present theory was extended so as to treat a system of nonadiabatic transition such as that in NaI molecule, whose ground and first excited potential curves intersect with each other due to intramolecular electron transfer. It has been shown for the first time that the bifurcation of nuclear wavepackets can be directly and experimentally observed with the pump-probe photoelectron spectroscopy. This is of great importance both in chemistry, wave-pacekt engineering, quantum chaos, the fundamental quantum theory, and so on.