Fast decay constant

Lin et al. [17] studied the dynamics of copolymers adsorbed on an air-water interface. These measurements complemented the static measurements described above and in Fig. 4. The extent of the polymer films perpendicular to the surface is small compared to penetration distance and wavelength so that EWDLS is most sensitive to variation of composition in the plane of the interface. Figure 7 shows the measured normalized autocorrelation I (/) for different surface pressures. Frames a-d were taken during the first compression of the monolayer, and frames e-h were taken during the second compression. The difference between the two sets of measurements is an indication of structural changes induced by compression cycling. The frames e-g can be compared to the data in Fig. 4. The solid lines in the three frames are fits to a sum of two exponential functions, each with a characteristic decay time. The fast decay constant has a characteristic associated with diffusive motion of the disks. The slow decay constant ( several seconds) was ascribed to the dynamics of the associations of disks. 

Therefore, VOC and SVOC emission profiles may differ depending on the factors mentioned as is demonstrated in Fig. 7 for moderate decay, fast decay, constant emission and increasing emission. All the studies were performed at 23 °C and 50% relative humidity. Even for the same type of products, the emission may be different over several orders of magnitude as is demonstrated in Fig. 8 for UV-cured furniture coatings. Here, chamber concentrations (2 VOC) were measured under identical conditions after 24 h and 672 h, respectively (see Ref. [43] for details). 

The fast decay constant is smaller for the as-received sample (170.4 ps) and most probably represents the effective nonradiative recombination at room temperature. The slow-decaying component is attributed to the radiative lifetime of the free exciton. The 0.86 ns value measured for the as-received sample is reasonably consistent with the 0.97 ns value measured by Koida et al. [176] for single-crystal ZnO. The relative magnitude of the slow-decaying component to the fast-decaying component (A2/A1 = 0.094 for 540 pj cm ) for the as-received sample suggests that the nonradiative processes are dominant. It has been proposed that the nonradiative... 

FIG. 12 Simulation of fluorescent decays for dye species located in the aqueous phase following laser pulses in TIR from the water-DCE interface according to Eq. (38). A fast rate constant of excited state decay (10 s ) was assumed in (a). The results showed no difference between infinitely fast or slow kinetics of quenching. On the other hand, a much slower rate of decay can be observed for other sensitizers like Eu and porphyrin species. Under these conditions, heterogeneous quenching associated with the species Q can be readily observed as depicted in (b). (Reprinted with permission from Ref 127. Copyright 1997 American Chemical Society.)... 

In order to directly probe the dynamics of CT between Et and ZG, and to understand how the intervening DNA base stack regulates CT rate constants and efficiencies, we examined this reaction on the femtosecond time scale [96]. These investigations revealed not only the unique ability of the DNA n-stack to mediate CT, but also the remarkable capacity of dynamical motions to modulate CT efficiency. Ultrafast CT between tethered, intercalated Et and ZG was observed with two time constants, 5 and 75 ps, both of which were essentially independent of distance over the 10-17 A examined. Significantly, both time constants correspond to CT reactions, as these fast decay components were not detected in analogous duplexes where the ZG was re-... 

The quantity k3 may be considered as an instrumental constant to be determined in a blank experiment—that is, without added solute. In this case, the current is given by I(t)/I(0) = (1 - vt/d) exp( - k3 t), from which k can be determined. With the solute added, the current initially decays exponentially (fast decay) from which is determined h + k2 + k3, while the ratio of the initial plateau to the initial current gives k2/(k] + k2 + k ). The detachment rate k2 is now obtained from the last two numbers, and then the attachment rate fe, is also obtained since k3 is already predetermined. In short, both attachment (kj and detachment (k2) rates are obtainable from the time dependence of the cell current following a brief pulse of ionizing radiation. 

Plastic phosphors are made by adding scintillation chemicals to a plastic matrix. The decay constant is the shortest of the three phosphor types, approaching 1 or 2 nanoseconds. The plastic has a high hydrogen content therefore, it is useful for fast neutron detectors. 

Analysis of the relative contributions of the slow and fast decays to the total intensity, by "peeling off the slower from the linear region of a semi-log plot of the autocorrelation function, indicates that it is the ordinary scattering that decreases in intensity. The extraordinary contribution remains roughly constant once it appears. 

The pseudorotaxane self-assembles through hydrogen bonding, and the binding constant, calculated using steady-state fluorescence, is 1.4 x 10. The zinc phthalocyanine derivative exhibited an excited-state lifetime of approximately 3.1 ns. The fast decay of the excited state of 1 ZnPc upon complexation with the fullerene... 

Two typical pump-probe transients of the ion signal are shown in Fig. 2. The transient data (points) have been fit using a function consisting of three components a growth (ti) and decay (x2) component (dashed line), a fast decay (T3) component (doted line), and a constant intensity plateau component that does not evolve with time (dot-dash line). 

The decay curve recorded at 515 nm was analyzed by the sum of two-or three-exponential functions. The fitting to the experimental data with a three-exponential function was always better that a two-exponential function. The fast decay component with a time constant of 1.1 ps (59%), corresponding to the fast rise time at 650 nm, and a very fast rise time of 70-110 fs (73%), were obtained in addition to the long decay component. From these results, it is concluded that the closed-ring form is mainly formed from the species with an absorbance maximum at 515 nm with a... 

The experimental results for v = 7 [37] showed that the lowest ( 15) rotational levels exhibited single exponential decay with a decay constant that was essentially independent of J. These levels were then assumed to be stable and unaffected by the predissociation. For much higher initial rotational states, J > 28, the observed lifetime was dramatically shortened. A very rapid initial decay was observed followed after a few microseconds by a slower decay. On increasing the pressure, the initial fast decay was hardly affected but the intensity of the longer-lived decay component increased as more molecules were transferred by rotational relaxation out of the initially formed predissociated state into lower-lying stable states. 

The rate of emission of photons from a scintillator is XNoeh, where N0 is the total number of photons emitted and X is the decay constant of the phosphor. For Nal(Tl) the decay time x (=A I) 220ns, whereas for fast plastic x 2ns (i.e., in the first ns 40% of the light from a plastic scintillator is typically emitted, whereas only 0.5% is emitted from Nal(Tl)). 

Cha et al. (1999) used a variant of FRET called LRET for lanthanide-based fluorescence energy transfer. In this technique (Selvin, 1996) the donor is terbium or europium which, in fact, is luminescent. There are several advantages of this technique over regular FRET. It has been found that terbium emits isotropically, which means that the uncertainty due to the dipole orientation is decreased to a maximum error of 10%. This error can be decreased even further if the anisotropy of the acceptor is also known. The second advantage is that the fluorescence decay has a time constant of about 1.5 ms, making it easily measurable with conventional recording techniques. The third advantage is that the emission of terbium is peaked and one can find fluorophores that emit in between peaks. This means that the fluorescence of the acceptor can be measured with little or no contamination from the donor. In addition, as the acceptor has a fast decay, any measurement of the acceptor fluorescence with decays comparable to the donor will exclude any possible direct... 

Some of these will be discussed in detail below. The effect of increasing temperature, instead of applying microwave fields on the relative bands originating from the different zf levels, is also used to detect the presence of the state of spin alignment (41). At temperatures for which the SLR processes have rates comparable to the unimolecular decay processes, the decay curve becomes sensitive to temperature. The decay constant of the phosphorescence at temperatures for which the SLR are fast is related to the unimolecular decay constants of the individual zf levels by the equation (42)... 

More recent measurements vary the energy of the pump and probe independently (Fauchet et al. 1986). Some data are shown in Fig. 8.9 for a 2.0 eV pump and different probe energies. The transient response of the induced absorption is almost constant when the probe energy is above 2 eV as found by Vardeny and Tauc, but there is a fast decay of the absorption at lower probe energies. The decay is interpreted in terms of the bleaching of the absorption transitions which occurs when a carrier occupies a conduction band state and so inhibits the excitation of electrons from the valence band. The transient absorption is the... 

---