Transitions nonradiative

A nonradiative transition between states of different multiplicity is called intersystem crossing  

NONRADIATIVE TRANSITIONS IN RARE EARTH IONS THE ENERGY-GAP LAW 

Internal conversion is a nonradiative transition between states of like multiplicity (e.g., singlet to singlet, triplet to triplet, but not singlet to triplet)  

As discussed in Chapter 1, the probability of a nonradiative transition is proportional to the square of the vibrational overlap integral J xiXa drv  

A further possibility is that molecules undergo a nonradiative transition from the excited singlet states to the triplet states (intersystem crossing). This is the origin of some loss mechanisms for dye lasers. 

M.L) it may be a MMCT state (see text). The arrow indicates the nonradiative transition from the charge-transfer state d to the ground state, so that c b and c - a emission is quenched 

Radiative and radiationless (nonradiative) transitions may be pictured as competing vertical and horizontal crossings, respectively, between the 

Figure 2 Variation of the quantum efficiencies of photodissociation of photoionization and of nonradiative transition to the ground state, r] r = l — — t]i, in liquid water as a function of

The above dynamical description of the polymerisation strongly parallels that of nonradiative transitions and this is not accidental althouth the monomer crystal from which the polymeric one is issued, do fluoresce, the polymeric one does not, despite its strong absorption at 2 eV. This strongly indicates efficient nonradiative relaxation of the excitation and strong electron-phonon coupling. 

Figure 2.6 An energy-level scheme for (a) four- and (b) three-level lasers, transition =, laser transitions , fast nonradiative transitions.

It has been possible to employ the heavy-atom solvent effect in determining the rate constants for the various intercombinational nonradiative transitions in acenaphthylene and 5,6-dichIoroacenaphthylene.<436,c,rate constants, which are not accessible in light-atom solvents due to the complexity of the mechanism and the low efficiency of intersystem crossing from the first excited singlet to the first excited triplet, can be readily evaluated under the influence of heavy-atom perturbation. 

Figure 5.61 summarizes the temperature behavior of decay time r and quantum efficiency xj of the blue luminescence from benitoite in the forms ln(r) and ln(q) as a function of reciprocal temperature 1/T. Figure 5.62.a demonstrates a suitable energy levels scheme. After excitation the metastable level 1 is populated due to nonradiative fast transition from excited level. Between levels 1 and 2 the equilibrium population is established due to nonradiative transition. The relative quantum yield of the blue emission may be described by simple Arrhenius equation  

Figure 9.1. A Jablonski diagram. So and Si are singlet states, Ti is atriplet state. Abs, absorption F, fluorescence P, phosphorescence IC, internal conversion and ISC, intersystem crossing. Radiative transitions are represented by full lines and nonradiative transitions by dashed lines

The mathematical definition of the Born-Oppenheimer approximation implies following adiabatic surfaces. However, software algorithms using this approximation do not necessarily do so. The approximation does not reflect physical reality when the molecule undergoes nonradiative transitions or two 

---