A microscopic theory for describing ultrafast radiationless transitions in particular for, photo-induced ultrafast radiationless transitions is presented. For this purpose, one example system that well represents the ultrafast radiationless transaction problem is considered. More specifically, bacterial photosynthetic reaction centers (RCs) are investigated for their ultrafast electronic-excitation energy transfer (EET) processes and ultrafast electron transfer (ET) processes. Several applications of the density matrix method are presented for emphasizing that the density matrix method can not only treat the dynamics due to the radiationless transitions but also deal with the population and coherence dynamics. Several rate constants of the radiationless transitions and the analytic estimation methods of those rate [Pg.183]

Recent rapid developments in ultrashort pulse laser [1-5] make it possible to probe not only the dynamics of population of the system but also the coherence (or phase) of the system. To treat these problems, the density matrix method is an ideal approach. The main purpose of this paper is to briefly describe the application of the density matrix method in molecular terms and show how to apply it to study the photochemistry and photophysics [6-9]. Ultrafast radiationless transactions taking place in bacterial photosynthetic reaction centers (RCs) are very important examples to which the proposed theoretical approach can be applied. [Pg.184]

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