Excitation-energy requirements

If the excitation energy required to fomi activated species A is much larger than k T its concentration will remain small. This is fulfilled if k Following Bodenstein, [A ] is then assumed to be quasi-stationary,... 

Nonradiative transfer of excitation energy requires some interaction between donor and acceptor molecules and occurs if the emission spectrum of the donor overlaps the absorption spectrum of the acceptor, so that several vibronic transitions in the donor must have practically the same energy as the corresponding transitions in the acceptor. Such transitions are coupled, i.e., they are in resonance, and that is why the term resonance energy transfer (RET) or electronic energy transfer (EET) are often used. 

The increase in energy of (pz in going over to can be traced to the excitation energy required to change from s character of pz to fully p character of tp3-... 

Macroscopic treatments of diffusion result in continuum equations for the fluxes of particles and the evolution of their concentration fields. The continuum models involve the diffusivity, D, which is a kinetic factor related to the diffusive motion of the particles. In this chapter, the microscopic physics of this motion is treated and atomistic models are developed. The displacement of a particular particle can be modeled as the result of a series of thermally activated discrete movements (or jumps) between neighboring positions of local minimum energy. The rate at which each jump occurs depends on the vibration rate of the particle in its minimum-energy position and the excitation energy required for the jump. The average of such displacements over many particles over a period of time is related to the macroscopic diffusivity. Analyses of random walks produce relationships between individual atomic displacements and macroscopic diffusivity. 

Excitation energy (AE) the excitation energy required to promote an electron from ground to excited state is... 

To describe the conductivity of an intrinsic semiconductor sample quantitatively, we need to calculate the concentrations of both types of charge carriers in the solid. The key quantity that controls the equilibrium concentration of electrons and holes in an intrinsic semiconductor is the band gap. Because the thermal excitation energy required to produce an electron and a hole is equal to Eg, the intrinsic carrier concentrations can be related to Eg using the Boltzmann relationship ... 

The decrease of the excitation energy required to form the pentavalent state of phosphorus as compared with nitrogen and its greater electropositive character, explains the readiness with which the tertiary phosphines undergo addition reactions with chlorine and sulphur. 

In this expression the enthalpy of H bond formation is designated by — W W —AH), Wq and W referring to the ground and excited states, respectively. The quantity wi is the excitation energy required by the Franck-Condon principle. Thus, the frequency shift gives the difference between the H bond enthalpy in the ground state and in the excited state plus the quantity w. Since w is always positive, the shift will always be more positive (more to the blue) than implied by Wo — Wiy whether Wo exceeds or is less than Wi,... 

Fig. 6 Exciton trapping on organic matrix molecules with subsequent energy transfer. Exploitation of matrix singlet and triplet excitation energy requires the effectiveness of two independent processes of energy transfer. Such a matching of molecular energies might be difficult to achieve, when OLED emitter layers are developed, vibr. vibrational...

The history of observations of the doubly-excited spectrum of He is comparatively recent, because of the rather high excitation energies required. The first observation of double excitations in He is due to Silverman and Lassettre [321]. The earliest high resolution spectrum was... 

Actual the hybrid, used to form the —R bond will be the particular admixture of s and p which gives the strongest bond relative to the excitation energy required. The other orbital, does not have to form a bond in —R, so that it could be a... 

If the vibrations are not localized, but instead the molecule vibrates as a unit, this is known as skeletal vibration. The excitation energy required for skeletal vibration is very closely dependent on the structure of the molecule. The associated bands are typical for the whole molecule. They are... 

The value of E, which can be interpreted as the excitation energy required to move a sodium ion from its normal position in the crystal, is 190 kJ mole". The conductivity remains very low, about 1 X lO" ohm" cm", even at 800°C, only a degree below the melting point. 

The coupling of LHCs to the RC, the final destination of excitation energy, requires special attention because of electrochemically reactive intermediates that are generated along the RC electron transfer chain and... 

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