Our knowledge of the process of photodissociation is built on a foundatin of molecular spectroscopy developed since the 1920’s. However, modern photodissociation dynamics has been mainly created by the introduction of laser light sources around 1970. This review of molecular photodissociation emphasizes findings based on techniques developed in the past ten-fifteen years. These include measurement of the energy dependence of the branching ratios of the yields of different photodissociation channels and the distribution of velocity and internal states of the fragments. The time scale of the separation of the fragments is shown to vary from the microsecond to the femtosecond regime depending on whether the dissociation is indirect or direct. Multiphoton dissociation can be incoherent or coherent. In the latter case, if two different optical phths can accomplish dissociation, changing the relative phase of the transition matrix elements of the two paths can control the branching ratio of different channels. The branching ratio can also be controlled by aligning the parent molecule in an electric field or by using successive ultraviolet and infrared transitions. The review concludes with some applications of photodissociation to the terrestrial atmosphere and to the generation of reactive radical sources.
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Department of Molecular Engineering and Graduate School of Global Environmental Sqtudies Kyoto University Kyoto 606-8501Department of Chemistry Columbia University New York NY 10027 USA;
