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Photochemical reactions transition state theory

It would be an advantage to have a detailed understanding of the glass transition in order to get an idea of the structural and dynamic features that are important for photophysical deactivation pathways or solid-state photochemical reactions in molecular glasses. Unfortunately, the formation of a glass is one of the least understood problems in solid-state science. At least three different theories have been developed for a description of the glass transition that we can sketch only briefly in this context the free volume theory, a thermodynamic approach, and the mode coupling theory. [Pg.100]

The determination of the properties of transition states of reacting molecules. Much of the theory of the rate of chemical reactions is based on the notion that the transformation from reactant to products passes through a particular geometry of the excited reactant molecule, called the transition state. Until recently there were no experimental tools with which the transition state could be studied, but it is now possible to determine some of the properties of transition states and thereby test theoretical models of the photochemical reaction. [Pg.891]

In photochemical reactions, it is desirable to classify the transition state according to its aromatic properties. In hydrocarbons, the excited states most likely to be involved are those in which an electron is transferred from a n-bonding orbital to a tt -antibonding orbital jt tt ), or in which an electron is transferred from a nonbonding orbital to a ff -antibonding orbital (n jt ). In principle, the excited states could be singlet or triplet states, but simple molecular orbital theory does not distinguish between the two. [Pg.57]


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