Intramolecular Vibrational Redistribution dark state

The language of bright state and dark state is central to population quantum beats and also to the related polyatomic molecule radiationless decay processes (Bixon and Jortner, 1968 Rhodes, 1983), Intramolecular Vibrational Redistribution (IVR) (Parmenter, 1983 Nesbitt and Field, 1996 Wong and Gruebele, 1999 Keske and Pate, 2000), Inter-System Crossing (ISC), and Internal Conversion (IC), discussed in Section 9.4.15. 

This two-state quantum beat example is identical to the doorway mediated non-radiative decay problem frequently encountered in polyatomic molecule Intramolecular Vibrational Redistribution (IVR), Inter-System Crossing (ISC), Internal Conversion (IC), and compound anticrossings. There is a single, narrow bright state. It couples to a single, broad, and dark doorway state. The width of the doorway state is determined by the rate of its Fermi Golden Rule decay into a quasi-continuum of dark states. 

J. Giraud-Girard, J. Manz, and Ch. Scheurer, Twist Dynamics of 9-(N-Carbazolyl)-Anthracene Effects of Intramolecular Vibrational Redistribution and Non-Adiabatic Transitions in Coupled Bright and Dark States , Z. Phys. D 39, 291 (1997). 

The concept of intramolecular vibrational energy redistribution (IVR) can be formulated from both time-dependent and time-independent viewpoints (Li et al., 1992 Sibert et al., 1984a). IVR is often viewed as an explicitly time-dependent phenomenon, in which a nonstationary superposition state, as described above, is initially prepared and evolves in time. Energy flows out of the initially excited zero-order mode, which may be localized in one part of the molecule, to other zero-order modes and, consequently, other parts of the molecule. However, delocalized zero-order modes are also possible. The nonstationary state initially prepared is often referred to as the bright state, as it carries oscillator strength for the spectroscopic transition of interest, and IVR results in the flow of amplitude into the manifold of so-called dark states that are not excited directly. It is of interest to understand what physical interactions couple different zero-order modes, allowing energy to flow between them. A particular type of superposition state that has received considerable study are A/-H local modes (overtones), where M is a heavy atom (Child and Halonen, 1984 Hayward and Henry, 1975 Watson et al., 1981). 

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