Structural Determination of the Short-lived Species by Time-resolved Electron Diffraction.

为了研究短寿命物种的分子结构，设计并建造了一台新的电子衍射仪。在该装置中，在传统装置的照相底片位置安装的NE102A型塑料闪烁体将衍射的电子转化为光子。在塑料闪烁体前面设置了一个固定的r^2扇区。通过放置在真空室外的光学透镜，在光学多通道分析器(大约700个通道)上收集光子。光学多道分析器有一个选通系统，可以提供高达20 ns的时间分辨率。另一方面，喷嘴管由石英制成，周围有四个Xe闪光灯(最大100 J/F)。最大为1F/S。脉冲持续时间为Ca。200微秒)，以便可以通过前体分子的闪光光解有效地生成诸如自由基和电子激发分子之类的短寿命物种。为了使闪光灯的触发脉冲和光学多道分析器系统的门脉冲具有一定的延迟同步，设计了电子电路，目前正在进行初步测试，以检查系统的性能。记录了CCl_4和CS_2的衍射图，具有良好的重复性。

A new electron diffraction apparatus has been designed and constructed in order to study the molecular structures of short-lived species. In this apparatus, the diffracted electrons are transformed into photons by an NE102A plastic scintillator which is set at the position of a photographic plate for the conventional apparatus. A fixed r^2-sector is set in front of the plastic scintillator. The photons are collected on an optical multichannel analyzer (ca.700 channels) by an optical lens put outside the vacuum chamber. The optical multichannel analyzer has a gating system which can provide time resolution of up to 20 ns.On the other hand, the nozzle tube is made of quartz and surrounded by four Xe flash lamps (100 J/F max. and 1F/S max. pulse duration is Ca. 200 mus) in order that short-lived species such as radicals and electronically excited molecules can be made efficiently by means of the flash-photolysis of precursor molecules. Electronic circuits are designed so that the trigger pulse of the flash lamps and the gate pulse of the optical multichannel analyzer system are synchronized with some amount of delay.At the present stage, a preliminary test is being carried out to check the performance of the system. The diffraction patterns of CC1_4 and CS_2 have been recorded with good reproducibility.