Radiationless Decay Rates of Initially Selected Vibronic States in Polyatomic Molecules

Radiationless Decay Rates of Initially Selected Vibronic States in Polyatomic Molecules 

Until now the discussion of electronic relaxation processes in large molecules embedded in an inert medium implicitly assumed that the nonradiative decay occurs from a manifold of thermally equilibrated levels of the initial electronic state. In the present section, we present an expression for the nonradiative decay probability of a single vibronic level of a large isolated molecule. We consider a molecule that has a set of zero-order selectable vibronic states, belonging to electronic 

Electronic relaxation in different excited vibronic levels corresponding to the same electronic configuration can be experimentally studied, provided that, as mentioned above, (1) single vibrational levels within the initial electronic state are populated and (2) the excited molecule decays nonradiatively on a timescale much shorter than the mean time between deactivating collisions or by other means such as infrared fluorescence [115]. For typical polyatomic molecules in the gas phase, a narrow-band optical excitation pulse (as small as 1 and shorter relative to the genuine decay times wiH result in the selection of a single vibronic state. U nder these conditions, 

The expression for the nonradiative decay rate of the optically prepared state sm ) now becomes 

Several comments should be made at this point. 

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