Franck-Condon pluck

In most vibrational wavepacket experiments, the time-evolving S (t) generally contains more than two vibrational eigenstates. The vibrational quantum numbers and t = to amplitudes of these vibrational eigenstates in k(t) are determined by the nature of the pluck that creates l (t) at f0. If the excitation-pulse is a simple, smooth, and short-time Gaussian, the result is a Franck-Condon pluck... 

As is ISC, IC is very slow for electronic states with similarly shaped potential energy surfaces. When the potential surfaces have very different shapes, there will be a small number of vibrational doorway states that are especially effective in coupling to the bright state. Conical intersections are a special class of potential surfaces of very different shapes. But even when potential surfaces have very different shapes, many normal coordinate displacements and the associated vibrational normal modes will have nearly identical forms on both surfaces. These normal modes are Franck-Condon inactive and do not contribute to IC. The normal coordinate displacements that express the differences in shapes of the potential surfaces are embodied in vibrational normal modes that are Franck-Condon active. These modes are called promoting modes because, when such a mode on one potential surface is plucked from an eigenstate on the other surface, intramolecular dynamics is promoted or initiated. 

Fig. 1. Franck-Condon spectrum for a two-dimensional uncoupled local mode Hamiltonian. The potential is of the form V(x) + V(y), where V is a Morse potential. The Franck-Condon factors (vertical lines) were computed for a wavepacket displaced along the x=y axis, i.e., along the symmetric stretch", which is an unstable mode of motion for this local mode system. The intensity pattern of Franck-Condon factors is such that, by smoothing the spectrum, we get a series of peaks at the energies of the normal mode "slice" of the potential, l/(s) E 2Y(s//l). Lesson The "pluck" we give the system is one thing, the intrinsic potential, quite another.

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