Relaxation lifetime

TR-SFG seems to be an ideal tool to study the surface dynamics of adsorbed CO at solid/liquid interfaces. Although there are several reports of TR-SFG studies on an electrode, they are only of investigations of vibrational relaxation lifetime by IR excitation [34, 65, 67]. 

Table 4 Relaxation lifetimes for the dissociation of 7-12 from DNA or polydeoxynucleo-tides104,105...

Mossbauer spectroscopy can only be used to obtain rates of interconversion if the lifetimes are close to 10 7 second. As described in Section III,E a few examples satisfying this condition have been found. Some questions remain over the quantitative interpretation of the data. Nevertheless, spin-equilibrium relaxation lifetimes have been estimated from Mossbauer temperature-dependent linewidths for two salts of an iron(III) complex, [Fe(acpa)2]+. The lifetimes are of the order 10 5—10 7 second over temperature ranges from 100 to 300 K (109, 111). 

When a fluorophore is bound to a protein, its fluorescence will be dependent on the polarity of the surrounding amino acids. Fluorescence spectra are also dependent on the rigidity of the medium. The relaxation phenomenon (reorientation of the dipole environment) occurs much more easily in a fluid medium. In such a case, emission will occur after relaxation. This is the case when relaxation is faster than fluorescence, i.e., the relaxation lifetime rr is shorter than the fluorescence lifetime to- This occurs when the binding site is flexible, and the fluorophore can move easily. Emission from a relaxed state does not change with excitation wavelength. This can be explained by the fact that whatever the value of the excitation wavelength, the emission will always occur at the same energy level. 

The pressure effects on spin relaxation dynamics for these iron(II) complexes have been examined using laser flash photolysis techniques. For Fe(pyim) the two spin states are in equilibrium with a K = 0.56 in 298 K acetone with a partial molar volume difference AV = +8.1 cm mol [34]. Photoexcitation (2ex = 532 nm) leads to transient bleaching of the low spin isomer s MLCT bands followed by first order relaxation to the original spectrum with a 45-ns lifetime. Transient bleaching and subsequent return of the MLCT absorption was attributed to formation of the HS isomer and subsequent spin relaxation. The pressure dependence of the relaxation lifetimes was used to determine the activation volumes of the spin relaxation rates for a variety of FeL in different solvents. It was found that AV j fell into a remarkably narrow range of values (-5.5 + 1 cm mol ) and it was concluded that the spin crossover for these species follows a common mechanism via a transition state located midway between the high and low spin states [33]. 

The effect of diffusion within isolated pores (allowing wq to vary) was first considered by Brownstein and Tarr. In the event that diffusion within a pore is not rapid, then more than one relaxation time will be observed for that pore, with values dependent on the detailed pore geometry (rather than simply the S/V ratio of that pore). The mean relaxation lifetime under conditions when... 

Fluorescence resonance energy transfer (FRET) experiments commonly use the fluorescent spectrum and relaxation times of the Forster donor and acceptor chromophores to find the distances between fluorescent dyes at labeled sites in protein, DNA, RNA, etc. FRET is a type of spectroscopic ruler . The computation uses either experimental quantum yields or relaxation lifetimes to calculate the efficiency of resonance energy transfer Ej. 

As mentioned earlier, this type of 3-regime behavior with bulk density — rapid change followed by a near invariance (or lesser change) followed by subsequent, more rapid change — is the characteristic signature of local density enhancement effects which has been observed in numerous spectroscopic studies [13,21,22,26,66-68]. Thus, the question naturally arises as to whether the observed vibrational relaxation behavior on the near-critical isotherm is a consequence of local density enhancements. The additional experimental evidence of such plateau behavior in infrared [68,76] and electronic [75] spectroscopic shifts for these same vibrational systems on the near-critical isotherm supports this conjecture, but is not conclusive, because no direct relationship has been shown between the presence of local density enhancements and vibrational relaxation lifetimes, or between local density enhancements and infrared spectroscopic shifts (although such a relationship has been demonstrated for electronic spectral shifts) [77]. 

To determine if there is a correlation between the observed local density enhancements in the model system and the computed relaxation lifetimes, we use isolated binary collision theory [81-83], which, although approximate, has some empirically established validity [75,82,84], to provide a framework for our analysis [12]. Specifically, the isolated binary collision theory yields an expression for the vibrational relaxation rate. 

It was Yasuoka et al. (1989) who suggested for the first time the presence of the spin gap based on experiment. They observed a sharp increase in the nuclear spin relaxation lifetime below T (T > T ) in the underdoped region. This was attributed to the opening of a spin gap . They presumed that the spin fi eedom of electrons dies down below T. Alloul et al. (1989) soon also assumed the spin gap fi om NMR Knight shift measurements. 

Duan CK, Reid MF (2007) Macroscopic models fm the radiative relaxation lifetime of luminescent centers embedded in surrounding media. Spectr Lett 40 237-246... 

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