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

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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.