高能光电子在CO、CO2 和CH3F 分子内禀坐标下的散射和衍射

As one of the most fundamental reaction processes, molecular photoionization provides a wealth of information about molecular strucnture and reaction dynamics, thus has continuously received a remarkable level of interest. Viewed from both theoretical and experimental side, the most natural reference frame for considering molecular photoionization is the molecular frame. That is the reason why the molecular frame photoelectron angular distribution MFPAD becomes one of the most important experimental techniques to explore the molecular photoionization. However, up to now, constrained by the available experimental techniques, most of MFPAD measurements concentrate on the photoionization with electron kinetic energy below 50 eV. As the result, quite amount of fundamental physical reaction mechanisms beyond observation, e.g. the multi-slit diffraction of photoelectron inside the molecule, the phase shift due to electron scattering, and determine single molecular structure by electorn diffraction, etc..Within this proposal, we will measure the MFPADs of CO, CO2, and CH3F molecules with high electron kinetic energy using the most recently upgraded EPICEA multi-coincidence setup at Synchtron SOLEIL in France. As the mesaurable electron kinetic energy can be as high as 800 eV, the de Broglie wavelength is smaller than the internuclear distance in the molecule, thus we obtain for the first time the diffraction pattern in space from a single molecule.

作为最基本的反应过程之一，分子光电离提供了丰富的结构和动力学信息，因此得到科学界长期的关注。研究分子光电离的最自然参照系是分子内禀坐标系，所以分子内禀坐标光电子角分布(Molecular Frame Photoelectron Angular Distribution MFPAD)成为现代研究分子光电离的最重要的手段之一。然而,迄今为止，限于实验手段，MFPAD实验中电子动能普遍低于50eV，很多基本物理过程的研究受到限制。例如光电子在分子内部的多缝衍射、衍射相移、以及通过电子衍射来确定分子结构等。. 在本项目申请中，利用最近申请人在法国工作时升级的SOLEIL同步辐射的EPICEA多重符合测量装置，我们将测量CO,CO2和CH3F分子的高动能的分子坐标下光电子角分布。由于电子动能提高到800eV，电子de Broglie波长小于分子核间距，将首次实验上得到单个分子的电子干涉条纹。

光电子衍射中，从某个元素原子发射的光电子可能被邻近原子弹性散射，电子波相干涉导致光电子角分布出现衍射极值。气体分子是最合适的简单体系研究对象。从离子的三维动量可以确定在电离时的分子取向。这样，从光子极化方向、分子空间取向、光电子三维动量，得到分子内禀坐标下的光电子角分布。在分子内禀坐标下的高动能光电子角分布可以细致分析光电子的散射和衍射机制。.在项目基金执行区间，我们申请到法国SOLEIL同步辐射实验室EPICEA高动能高分辨多重符合测量装置的5次实验时间：.1..O2: Identify of hidden atomic decays in the resonant Auger processes after core excitation of O2.2..CH3F: Charge transfer during ultrafast dissociation of molecules.3..CO2: Direct observation of photoelectron diffraction following C1s and O1s photoionization of CO and CO2 molecules.4..CF4: Explore ultrafast dissociation in CF4 molecule with the momentum of fragments resolved.5..N2: Young's double-slit experiment from vibrating diatomic N2 molecule.其中O2的实验数据已经处理完，其初步结果分别在Sci. Rep.和Phys. Rev. A上发表，最终结果的论文正在撰写中。CO2部分结果发表在J. Chem. Phys. 。其他的数据已经有初步分析结果。在已经发表的结果中.1..将O2分子高度重叠Auger能谱按照O1s电离的自旋轨道劈裂分开，证明自旋轨道劈裂不同分支对应的Auger谱不只是强度不同，而且还需要Auger过程的选择性。.2..研究了O2共振Auger后进一步发生的解离和电离，发现这些动力学过程非常丰富和复杂，有些态不解离，而解离中常常伴随不同势能曲线间的交叉和避免交叉。.3..分子坐标下的光电子角分布可以用来确定CO2分子中的C-O键长。