Quantum states, decay rates

An interesting question is whether the large fluctuations in the quantum mechanical decay rates have an influence on the temperature and pressure dependent unimolecular rate constant P) defined within the strong collision model, in Eq. (2). In the state-specific quantum mechanical approach the integral over the smooth temperature dependent rate k E) is replaced by a sum over the state-specific rates fc,-. Applications have been done for HCO [93], HO2 [94-96], and HOCl [97]. The effect of a broad distribution of widths is to decrease the observed pressure dependent rate constant as compared to the delta function-like distribution, assumed by statistical theories [98,99]. The reason is that broad distributions favor small decay rates and the overall dissociation slows down. This trend, pronounced in the fall-of region, was clearly seen in a study of thermal rate constants in the unimolecular dissociation of HOCl [97]. The extremely... 

In this paper we examined quantum aspects of special classical configurations of two-electron atoms. In the doubly excited regime, we found quantum states of helium that are localized along ID periodic orbits of the classical system. A comparison of the decay rates of such states obtained in one, two and three dimensional ab initio calculations allows us to conclude that the dimension of the accessible configuration space does matter for the quantitative description of the autoionization process of doubly excited Rydberg states of helium. Whilst ID models can lead to dramatically false predictions for the decay rates, the planar model allows for a quantitatively reliable reproduction of the exact life times. 

The very low multiphonon decay rates obtained in Example 6.2 from the Po (Pr +) and p5/2 (Yb +) states are due to the large number of effective phonons that need to be emitted -14 and 38, respectively - and so the high-order perturbation processes. As a consequence, luminescence from these two states is usually observed with a quantum efficiency close to one. On the other hand, from the F3/2 state of Er + ions the energy needed to bridge the short energy gap is almost that corresponding to one effective phonon hence depopulation of this state to the next lower state is fully nonradiative. 

Since the radiative lifetime is nearly independent of v (852), it can be seen that the measured decay rate 1/t is proportional to kp, which in turn is proportional to the quantum yield of I atom production. Therefore, the wavelength dependence of decay rate follows approximately the quantum yield curve shown in Fig. V-22, that is, the decay rate is faster when the quantum yield of atom production is larger. However, the exact correspondence may not be expected, since both the B3n and ln states contribute to the 1 atom production, while only the B3n state gives rise to fluorescence. Then the percent absorption due to a transition to the B3fl state must be known at each wavelength. 

The rates km cover the km o accounting for the excited state decay of chromophore m (by radiative as well as non-radiative transitions) and the SC ) originated by inter-system crossing to triplet states (ISC rate). The simple km do not include the effect of excited state wave function delocalization and a possible decay out of exciton states [45], Therefore, we shortly demonstrate the computation of the photon emission part of the km including such a delocalization effect (determination of excitonic augment rates). It will be important for the mixed quantum classical simulations discussed in the following (for more details see also [11]). 

The absence of an enormous enhancement in radiative decay rates in the nanocrystals can also be verified by electronic absorption spectroscopy. The original claim stated that the Mn2+ 47) —> 6A1 radiative decay lifetime dropped from xrad = 1.8 ms in bulk Mn2+ ZnS to xrad = 3.7 ns in 0.3% Mn2+ ZnS QDs ( 3.0 nm diameter) (33). This enhancement was attributed to relaxation of Mn2+ spin selection rules due to large sp-d exchange interactions between the dopant ion and the quantum-confined semiconductor electronic levels (33, 124— 127). Since the Mn2+ 47 > 6Ai radiative transition probability is determined... 

In conclusion, the quantum-state dependence of the dissociation rate reveals a lot of detailed information on the decay of van der Waals complexes and allows to accurately ascertain parts of the multi-dimensional PES. 

Since the initial reports of the C-P-Q triads, a number of other molecules of the D-D -A or D -D-A types have been described. Triad 12, prepared by Wasielewski and coworkers, is a relative of the C-P-Q series in which the secondary donor is an aniline derivative (D), rather than a carotenoid [63]. The bicyclic bridges were introduced in order to add rigidity to the system. The fluorescence lifetime of the porphyrin moiety of 12 was found to be <30ps. This result is consistent with rapid electron transfer to the quinone to yield D-P+-QT. This result was confirmed by transient absorption measurements. The absorption results also revealed that this intermediate charge separated state decays with a rate constant of 1.4 x 1010 s-1 to a final charge separated state D+-P-Qr. Thus, the decay pathways are similar to those shown in Fig. 3 for the C-P-Q triads. This final state has a lifetime of 2.45 ps in butyronitrile (which is similar to that found for 4 in acetonitrile) [44], and is formed with a quantum yield of about 0.71. Thus, the efficiency of the transfer analogous to step 4 in Fig. 3 for this molecule is also about 0.71. 

By means of time-resolved fluorescence studies we were able to determine the C60 fluorescence deactivation rates, as 2.1 x 1010 s-1 in 9a, 6.6 x 109 s 1 in 9b and 1.3 x 109 s-1 in 9c. Importantly, the indulging trend resembles the relationship between the quantum yields of the conjugates (9a-d) and reference (1). In short, an intensified excited-state deactivation emerges with decreasing bridge length. However, no measurable decay rates were found for the trimer 9d. Conclusively, the indirect or direct population of Cgo possibly leads to an exothermic electron-transfer reaction, resulting in the radical-ion-pair state ... 

Spin-orbit coupling not only governs the amount and pattern of ZFS of the emitting triplet state, but it is also of dominant importance for the radiative emission decay rates and thus for the photoluminescence quantum yields. These properties are crucial for the suitability of triplet emitters in OLEDs. In conclusion, detailed spectroscopic studies of compounds triplet state properties in combination with... 

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