Deexcitation effect

Note that, as discussed at length in Chapter VI, this equation has to be limited to providing information on (nonlinear term on the time evolution of (canonical equilibrium. This type of equation lends itself to a qualitative description of deexcitation effects as observed by computer simulation. This is described further in Section IV.A with reference to the general analytical constraints imposed by RMT on any theory of the molecular Uquid state. 

The powerful continued fraction procedure (CFP) described by Grosso and Pastori Parravicini in Chapter III may be used to solve Eqs. (3) and (4). An alternative approach has been provided by Ferrario et al., who have computed a variety of numerically derived orientation and velocity acFs for a simple cosine potential and the more comphcated cosinal itinerant oscillator, another RMT-allowed structure. In Chapter VI, Ferrario et al. describe deexcitation effects from the two-dimensional disk-annulus itinerant oscillator also studied by Brot and coworkers. ... 

The difficulty in proving the exact nature of prethermal reactions is that they occur too fast for standard solid-state chemical methods. One attractive idea was expressed by Harbottle 29), namely that, if a strong isotope effect is shown, very little subsequent chemical influence can have been felt and the observed species must have been formed by prethermal processes. The supposition here is that isotopic differences come only from differences in the nuclear deexcitation pattern (total energy, y-ray cascades, angular... 

The calorimetric method of detecting EEPs is based on measurements of the thermal effect arising on surfaces featuring high efficiency of deexcitation. This technique was used for evaluating 02( A ) [31] of a... 

A third possible channel of S state deexcitation is the S) —> Ti transition -nonradiative intersystem crossing isc. In principle, this process is spin forbidden, however, there are different intra- and intermolecular factors (spin-orbital coupling, heavy atom effect, and some others), which favor this process. With the rates kisc = 107-109 s"1, it can compete with other channels of S) state deactivation. At normal conditions in solutions, the nonradiative deexcitation of the triplet state T , kTm, is predominant over phosphorescence, which is the radiative deactivation of the T state. This transition is also spin-forbidden and its rate, kj, is low. Therefore, normally, phosphorescence is observed at low temperatures or in rigid (polymers, crystals) matrices, and the lifetimes of triplet state xT at such conditions may be quite long, up to a few seconds. Obviously, the phosphorescence spectrum is located at wavelengths longer than the fluorescence spectrum (see the bottom of Fig. 1). 

Fluorescence and phosphorescence are particular cases of luminescence (Table 1.1). The mode of excitation is absorption of a photon, which brings the absorbing species into an electronic excited state. The emission of photons accompanying deexcitation is then called photoluminescence (fluorescence, phosphorescence or delayed fluorescence), which is one of the possible physical effects resulting from interaction of light with matter, as shown in Figure 1.1. 

Considering that the effective phonons in LaClj are those with an energy of 260 cm (see the caption to Figure 6.6), and considering the different energy gaps from the" p3/2 (Er +), Pq (Pr ), and" F5/2 (Yb +) energy levels, we determine the number, p, of effective phonons in each noiuadiative deexcitation process ... 

The method of moments of coupled-cluster equations (MMCC) is extended to potential energy surfaces involving multiple bond breaking by developing the quasi-variational (QV) and quadratic (Q) variants of the MMCC theory. The QVMMCC and QMMCC methods are related to the extended CC (ECC) theory, in which products involving cluster operators and their deexcitation counterparts mimic the effects of higher-order clusters. The test calculations for N2 show that the QMMCC and ECC methods can provide spectacular improvements in the description of multiple bond breaking by the standard CC approaches. 

Figure 15. Time-dependent behavior of OH(t> = 1-5) observed following production of the radical by the 0( D) + H2S reaction. The data, taken at 50- s intervals, clearly show the effects of vibrational cascade by collisional deexcitation of the initially produced inverted distribution. Reproduced with permission from Ref. 45.

If J" —> J excitation is accompanied or followed by deexcitation J —> J" in a stimulated emission process (SEP), then the population efficiency of the level can be increased considerably. It is now known [248, 347] that the process might be made more effective by applying the A-configuration scheme in which the first-step (J" — J ) excitation pulse is applied after the second-step (J — J") pulse which, at first glance, seems surprising. This process is called stimulated Raman scattering by delayed pulses (STIRAP). The population transfer here takes place coherently and includes coordination of the Rabi nutation phase in both transitions. 

The limitation in the determination of the strong interaction width is mainly given by the Doppler effect caused by the so-called Coulomb deexcitation acceleration. 

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