Formation and decay of superexcited molecules as studied by synchrotron-radiation photon and electron collisions

1.用同步辐射光子碰撞研究双激发分子我们测量了在甲烷、氨、水和乙烯的光激发下，中性碎片在紫外和可见光范围内发出荧光的截面绝对值与入射光子能量在10-40 eV范围内的函数关系。有趣的是，双激发态甲烷、氨和水的巴尔默荧光的振子强度与这些分子附近的单孔单电子超激发态的强度相当，这有力地表明了独立电子模型的破裂。在巴尔默荧光的横截面曲线中发现了双激发乙烯的重要作用。用重合电子-能量损失谱法研究超激发态分子重合电子-能量损失谱法是研究超激发态分子的一种很好的方法，是本课课组几年前发展起来的。电子能量损失谱的测量与电子与分子碰撞时中性碎片的真空紫外荧光的发射一致，其中显示了归因于超激发态的结构。在不同的入射电子能和散射角下，测量了氮分子、氧分子和甲烷分子在价态范围内的重合电子能损失谱。有趣的是，氮的光学禁止双激发态比允许双激发态贡献更大。为了详细地研究超激发态氧分子，测量了氧的时间分辨同步电子能量损失谱。在25 eV以上的范围内发现了双激发甲烷的强烈峰。第二代系统配备了位置敏感的电子探测器，可以更有效地获得光谱

1.Doubly excited molecules as studied by synchrotron-radiation photon collisionsWe have measured the absolute values of the cross sections for the emission of fluorescences in the ultraviolet and visible ranges from neutral fragments in the photoexcitation of methane, ammonia, water and ethylene as a function of incident photon energy in the range 10-40 eV. Interestingly, the oscillator strengths for Balmer fluorescences from doubly excited methane, ammonia and water in the inner valence range amount to the magnitudes comparable to those from nearby single-hole one-electron superexcited states of these molecules, which is a strong indication of the breakdown of the independent electron model. An important role of the doubly excited ethylene has been found in the cross section curves for Balmer fluorescences.2.Superexcited molecules as studied by the coincident electron-energy-loss spectroscopyThe coincident electron-energy-loss spectroscopy is an excellent means for investigating the s … More uperexcited molecules, which was developed by our group a few years ago. The electron energy-loss spectra are measured in coincidence with the emission of the vacuum-ultraviolet fluorescences from neutral fragments in electron collisions with molecules, in which the structures attributed to the superexcited states are shown up. We have measured the coincident electron-energy-loss spectra of molecular nitrogen, molecular oxygen, and methane in the valence range at several incident electron energies and scattering angles. Interestingly the optically-forbidden doubly excited states of nitrogen give larger contribution than the allowed doubly excited states. The time-resolved coincident electron-energy-loss spectra of oxygen have been measured to study the superexcited oxygen molecules in detail. The intense peaks attributed to the doubly excited methane have been found in the range above 25 eV. The second-generation system equipped with a position-sensitive detector for electrons has been developed to obtain the spectra much more efficiently Less