Studies of the dynamics of reactive molecules by the transient grating method over a wide time range

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The output of a dye laser pumped by a mode-locked YAG laser was divided into three, two of which were utilized to produce subpico second UV pulses by taking second the harmonics. These two pulsed-laser lights were crossed at the sample to produce a transient grating (TG) of excited molecules, and the remaining light was used as a probe light. In this way we have constructed a system to perform TG experiments in the subpico second range. We have also constructed a TG system for pico to nano second experiments using the third harmonics of a dye laser pumped by a pico second YAG laser. With these systems we are now equipped to do TG experiments over a very wide range of time from mili to subpico second. The following studies were made using these setups.(1) Studies in the picosecond range ; (1.1) Excited state dynamics of the molecules with very efficient nonradiative processes such as nitrobenzene and its derivatives and 9,10-diazaphenanthrene were clarified. (1.2) We have succeeded in d … More etecting the grating produced by the change in the refractive indecex due to the temperature change which appears instantaneously with the release of heat. Fast dynamics of Fe (III) in water and 2-hydroxybenzophenone in a SDS micellar solution were in vestigated by using this type of grating. (1.3) Rates of the electron transfer reaction in the hexamethylbenzene/tetracyanoethylen complex in supercritical CO_2 were determined at different solvent densities. The results were compared with the theoretical prediction.(2) New developments in the TG experiments in the mili to microsecond region : (2.1) Further studies on the radical diffusion were made to clarify the reason why radicals diffuse more slowly compared with parent molecules. (2.2) A new method to determine changes in enthalpy and reaction volume in a photochemical reaction was developed and applied to study the reaction of diphenylcyclopropane. (2.3) The TG method was used for the first time to study transport properties and reaction dynamics in a supercritical liquid. Less