Dynamics of highly-excited bolecules as studied by electron spectroscopy

我们建立了一种新的实验技术来证实由电子碰撞产生的高激发分子的动力学。该技术是电子能量损失光谱，与高激发分子的中性解离产生的碎片原子的光子检测相吻合。将此方法应用于最简单的氢分子（H_2），测量了与H （2p）形成一致的电子能量损失谱。我们所取得的成就如下。在单电子激发态的能量损失区测量了H_2的电子-能量损失谱。在较低的撞击能量下，光谱的形状发生了很大的变化。有趣的是，这种变化出现在能量损失的有限区域。我们的结论是，这种变化归因于禁态的出现，这些禁态很可能解离成H(1s)+H（2p）。所涉及的禁止状态已被确定，解离机制已被澄清。在双激发态的能量损失区测量了H_2的电子-能量损失谱。在光谱中可以看到两个宽峰，它们属于双激发态。这是在电子能量损失谱中首次观察到H_2的双激发态。两个峰中的一个可以用已知的光学允许的双激发态来解释。另一方面，另一个峰归因于禁止双激发态。然而，双激发态的前驱是未知的。我们的调查激发了许多理论家。综上所述，一致电子能量损失谱已被证明是证实由电子碰撞产生的高激发分子动力学的有用工具。

We have established a new experimental technique to substantiate the dynamics of highly-excited molecules produced by electron collisions. The technique is electron energy loss spectroscopy in coincidence with the detection of the photons from the fragment atoms produced through the neutal dissociation of the highly-excited molecules. This method has been applied to hydrogen (H_2), the simplest of molecules, and the electron-energy-loss spectra in coincidence with H (2p) formation have been measured. What we have accomplished is as follows.1. The coincident electron-energy-loss spectra of H_2 have been measured in the energy-loss region of single-electron excited states. There is a large change in the shape of the spectra on going to the lower impact energy. Interestingly, this change is seen in the limited region of the evergy loss. We have concluded that the change is ascribed to the appearance of the forbidden states which are likely to dissociate into H(1s)+H(2p). The forbidden states involved have been identified and the dissociation mechanism has been clarified.2. The coincident electron-energy-loss spectrum of H_2 has been measured in the energy-loss region of doubly excited states. Two broad peaks are seen in the spectrum which are ascribed to the doubly excited states. This is the first observation of the doubly excited states of H_2 in electron energy-loss spectra. One of two peaks is explained by the known optically allowed doubly excited states. On the other hand the other peak is ascribed to the forbidden doubly-excited states. The precursor doubly-excited states, however, are left unknown. Our investigation has been stimulating many theoreticians.In conclusion the coincident electron-energy-loss spectroscopy has proved to be a useful tool to substantiate the dynamics of highly-excited molecules produced by electron collisions.