Intramolecular radiationless

Internal conversion involves intramolecular radiationless transitions between vibronic states of the same total energy (isoenergetic states) and the same multiplicity, for example S2(v = 0) -Wr Si(v = n) and T2(v = 0) -Wr Ti(v = n). Typical timescales are of the order of 10 14-10 11s (internal conversion between excited states) and 10 9-10 7s (internal conversion between Si and S0). 

Bixon, M., and Jortner, J. (1968), Intramolecular Radiationless Transitions, J. Chem. Phys. 48, 715. 

Rh(bpyL3+ is an example of a complex that exhibits an almost pure n-n phosphorescence and demonstrates one of the limitations of nearly pure ligand localized emissions. At 77K, the complex is highly emissive with a beautifully structured blue ligand phosphorescence (Amax = 446 nmfor the first peak) having at in the tens of msec,(17) but it has no detectable room temperature emission. It is this very long radiative lifetime that causes the absence of room temperature emission. The radiative decay is so slow that it cannot compete effectively against inter- and intramolecular radiationless decay at room temperature. 

This expression, it may be recalled, is similar to the one obtained for intramolecular radiationless transfer rate for internal conversion and intersystem crossing (Section 5.2.1). For intermolecular cases... 

Observable effects in the quenching of fluorescence are usually the result of competition between radiation and bimolecular collisional deactivation of electronic energy, since vibrational relaxation is normally so rapid, especially in condensed phases, that emission derives almost entirely from the ground vibrational level of the upper electronic state. The simplest excitation-deactivation scheme, which does not allow for intramolecular radiationless... 

In the more complex situation where intramolecular radiationless processes occur as well as radiative and collisional ones, the equation becomes... 

Capture may take place to bound states of the negative ion that undergo radiationless transitions to repulsive states of the negative ion resulting in dissociative electron capture. These radiationless intramolecular transitions (Auger transitions) are a result of overlap of the discrete states with a continuum of states of AB-. These types of processes are illustrated for diatomic molecules in Figure 2.2b. Electrons are first captured into the bound state represented by curve 1, and before autodetachment can take place an intramolecular radiationless transition occurs to curve 2 resulting in dissociation into A and B-. 

We consider three decay channels for D in addition to injection Fluorescence (rate constant k ), intramolecular radiationless decay (rate constant k ), and energy transfer quenching within the adsorbed layer (rate constant kg) ... 

The processes of energy acquisition, storage and disposal in clusters are of considerable interest in their own right and also for the interpretation of similar processes in finite systems. Consider vibrational energy excitation of an intramolecular vibration of a molecule in a cluster, or of a cluster inter-molecular mode(s), which can be accomplished by collisional excitation, photoselective vibrational excitation, electronic excitation followed by intramolecular radiationless transitions or exciton trapping.178 In charged clusters... 

M.Bixon,J.Jortner,Intramolecular radiationless transitions, J.Chem. Phys.48 (1968) 715. 

For the selective enhancement of the wanted reaction channel by laser excitation of the reactants, the time span At between photon absorption and completion of the reaction is of fundamental importance. The excitation energy n hco (n = 1,2,...) pumped by photon absorption into a selected excited molecular level may be redistributed into other levels by unwanted relaxation processes before the system ends in the wanted reaction channel. It can, for instance, be radiated by spontaneous emission, or it may be redistributed by intramolecular radiationless transitions due to vibrational or spin-orbit couplings onto many other nearly degenerate molecular levels. However, these levels may not lead to the wanted reaction channel. At higher pressures collision-induced intra- or intermolecular energy transfer may also play an important role in enhancing or suppressing a specific reaction channel. 

Therefore, eoupling of the radiant state s> with the complex nonradiant manifold, when treated statistically, gives rise to an increase of homogeneous broadening, with a corresponding decrease of the lifetime of this zero-order state. The intramolecular radiationless damping constant yj" is similar in nature to the radiationless collisional damping constant yr. 

Lefebvre, R. (1971) Preparation and decay of initial states in intramolecular radiationless processes. Chem. Phys. Lett., 8, 306. 

Lefebre, R. and Savolainen, J. (1969) Photon echoes with molecules undergoing intramolecular radiationless transitions. Chem. Phys. Lett., 31, 449. 

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