Dynamics of relaxation

Theoretical and time-resolved spectroscopic studies of triene photochemistry The dynamics of relaxation of the excited singlet states of E- and Z-l,3,5-hexatriene (HT) have recently been studied in the gas phase and in solution. In the gas phase, population of the 21 / state of the Z-isomer by internal conversion from the spectroscopic 11B state has been estimated to occur with a lifetime Tig of about 20 fs, while the lifetime of the 21 / state has been determined to be T2A =730 fs47. The lifetime of the latter in ethanol solution has been determined by Fuss and coworkers to be T2a = 470 fs52. A similar 21A lifetime has been reported for -l,3,5-hexatriene in cyclohexane and acetonitrile solution by Ohta and coworkers48. 

It should be noted that the dynamics studied by fluorescence methods is the dynamics of relaxation and fluctuations of the electric field. Dipole-orientational processes may be directly related to biological functions of proteins, in particular, charge transfer in biocatalysis and ionic transport. One may postulate that, irrespective of the origin of the charge balance disturbance, the protein molecule responds to these changes in the same way, in accordance with its dynamic properties. If the dynamics of dipolar and charged groups in proteins does play an important role in protein functions, then fluorescence spectroscopy will afford ample opportunities for its direct study. 

In two-parametric families three constants can meet. If three smallest constants kj,ki and L have comparable values and are much smaller than others, then static and dynamic properties would be determined by these three constants. Stationary rate w and dynamic of relaxation for the whole cycle would be the same as for 3-reaction cycle A B C A with constants kj,ki and km- The damped oscillation here are possible, for example, if kj — ki—km—k, then there are complex eigenvalues X— k(—(3/1) 1( /3/ )). Therefore, if a cycle manifests damped oscillation, then at least three slowest constants are of the same order. The same is true, of course, for more general reaction networks. 

Dynamic Mechanical Relaxations in Glassy Polymers 3.1 Dynamics of Relaxations... 

It is mostly used to describe the effect of temperature on the dynamics of relaxation processes in glassy polymers. Rearranging Eq. (8), we obtain the relation between the activation energy AU (in kJ) and the temperature of relaxation, Tr(f), detected at frequency f ... 

Theoretical and time-resolved spectroscopic studies of triene photochemistry The dynamics of relaxation of the excited singlet states of E- and Z-l,3,5-hexatriene... 

Although we are unable to use the master equation approach to examine the dynamics of relaxation from the liquid-like state because a statistical method that can account for the dynamical contribution from the huge number of liquid-like minima has not yet been developed, we are able to illustrate the type of processes that would operate by examining relaxation from the highest-energy minima in our sample (Fig. 1.14). The probability... 

The dynamics of relaxation for single porphyrin molecules are illustrated by the Jablonski diagram in Figure 11.6. According to the Frank-Condon approximation, light absorption leads to electronic transitions in which the momentum... 

Clarke, J. F., McChesney, M. Dynamics of Relaxing Gases. London and Boston Butterworths, 1976, p. 300. 

In the last chapter, we used a steady-state treatment to relate the shape of an absorption band to the dynamics of relaxations in the excited state. Because a period on the order of the electronic dephasing time will be required to establish a steady state, Eqs. (10.43) and (10.44) apply only on time scales longer than this. We need to escape this limitation if we hope to explore the relaxation dynamics themselves. Our first goal in this chapter is to develop a more general approach for analyzing spectroscopic experiments on femtosecond and picosecond time scales. This provides a platform for discussing how pump-probe and photon-echo experiments can be used to probe the dynamics of structural flucmations and the transfer of energy or electrons on these short time scales. 

The orienting effect of a magnetic field on comb-shaped LC polymers was demonstrated in nuclear magnetic resonance experiments [28, 29, 32, 34, 35]. In this case, the magnetic field first acts as a means of creating an oriented structure and second, NMR permits obtaining information on the dynamics of relaxation processes and the character of the molecular ordering in LC polymers. 

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