Study on Multielectron Effect Near Molecular Inner-Shell Photoionization Thresholds

UVSOR的双环面分析仪（DTA）最初是由一个法国小组开发的，一直处于调节状态。没有任何出口狭缝的成像探测使我们能够同时观察到超过10%通过能量范围内的电子，以及它们的角度分布。最近，经过DTA的重新组装和精心调整，分析仪的性能得到了很大的提高。采用二维探测器的离子飞行时间谱仪正处于规划阶段，用于进行能量选择电子-离子重合实验。在研究和开发新的实验装置的同时，对分子内壳激发后的小产物，如高激发的中性物质和阴离子进行了一些试验。在N_2分子的1s阈值附近观察到由于N^*形成的强增强。已经发现，导致N^*形成的高激发态N_2^<+^*>是由核心激发态的旁观俄歇衰变和缓慢的光电子重新捕获到里德伯轨道所填充的。结果表明，亚稳态观测是研究核激发态衰变动力学和碰撞后相互作用引起的光电子重获的一种新的灵敏工具。对于分子内壳激发后的阴离子成像检测，我们在消除电子的大背景噪声方面遇到了困难，这可以通过进行时间分辨实验来解决。

The double toroidal analyzer (DTA) at UVSOR, which has been originally developed by a French group, has been under conditioning. The imaging detection without any exit slit enables us to observe electrons within an energy range more than 10% of the pass energy, and their angular distributions simultaneously. Recently it was confirmed that the performance of the analyzer has been improved considerably, after re-assembling of DTA and its careful tuning. The introduction of an ion time-of-flight spectrometer with a two dimensional detector is in the planning stage, to perform energy-selected-electron-ion coincidence experiments.Parallel to the research and development of new experimental setups, some trial experiments have been made for observing minor products, such as highly excited neutral species and anions after the molecular inner-shell excitations. A strong enhancement due to the N^* formation has been observed around the 1s threshold of N_2 molecules. It has been found that the highly excited N_2^<+^*> states leading to the N^* formation are populated by spectator Auger decay from the core-excited states, as well as by the recapture of slow photoelectrons into the Rydberg orbitals. It turns out that the metastable observation is a new and sensitive tool to study the decay dynamics of core-excited states and the photoelectron recapture due to the post-collision interaction. Concerning the anion imaging detection after the molecular inner-shell excitations, we have confronted difficulty in eliminating a large background noise by electrons, which may be fixed by performing time-resolved experiments.