Lifetime observed

Such long lifetimes are puzzling in view of the well-known n3 scaling of Rydberg state lifetimes observed from linewidths of resolvable series and predicted by theory. The n3 scaling derives from a fundamental property of Rydberg states. The normalization factor in the radial part of the Rydberg orbital scales as n 3/2. Thus... 

A fascinating insight into the impact that modelling can make in polymer science is provided in an article by Miiller-Plathe and co-workers [136]. They summarise work in two areas of experimental study, the first involves positron annihilation studies as a technique for the measurement of free volume in polymers, and the second is the use of MD as a tool for aiding the interpretation of NMR data. In the first example they show how the previous assumptions about spherical cavities representing free volume must be questioned. Indeed, they show that the assumptions of a spherical cavity lead to a systematic underestimate of the volume for a given lifetime, and that it is unable to account for the distribution of lifetimes observed for a given volume of cavity. The NMR example is a wonderful illustration of the impact of a simple model with the correct physics. 

Ex-situ generation. In this approach the radicals are generated away from the epr cavity under well-defined voltammetric conditions and then transferred into the epr cell (usually via a flow system). Such a method imposes a restriction on the radical lifetimes observable due to the dead time involved between generation and detection. 

However, the published corrosion rates of Ru from oxygen evolution are not reliable, as they forecast [50] Ru losses as high as 40 g cm-2 h, which is inconsistent with the anode lifetimes observed in commercial chlor-alkali cells. 

The 475 nm species (C) is observed with even longer lifetime (55 ns) in the absence of OH . Since the lifetimes observed are quite similar to that from a quenching study and since obviously this transient is quenched by OH , this... 

Photochemistry can be used to demonstrate solvent effects in supercritical fluids. The analysis revealed trimodal fluorescence lifetime distributions near the critical temperature, which can be explained by the presence of solvent-solute and solute-solute clustering. This local aggregation causes an increase in nonradiative relaxations and, therefore, a decrease in the observed fluorescence lifetimes. Concentration and density gradients are responsible for these three unique lifetimes (trimodal) in the supercritical fluid, as contrasted with the single lifetime observed in a typical organic solvent. The... 

In fact, with small particles or clusters, a range of excited state lifetimes could be observed by spectroscopic methods . The observed non-Arrhenius dependence indicated the importance of multiphonon electron tunnelling, probably to preexistent traps. The shorter lifetimes observed at shorter emission wavelenths indicated significant coulombic interaction between traps. 

Precise measurements of the excited state lifetimes of the DNA constituents were not available till very recently, mainly due to the limited time resolution of conventional spectroscopic techniques. Studying the DNA nucleosides by transient absorption spectroscopy, Kohler and co-workers observed a very short-lived induced absorption in the visible which they assigned to the first excited state [5,6]. The lifetimes observed were all well below 1 picosecond. The first femtosecond fluorescence studies of DNA constituents were performed using the fluorescence upconversion technique. Peon and Zewail [7] reported that the excited state lifetimes of DNA/RNA nucleosides and nucleotides all fall in the subpicosecond time, thus corroborating the results obtained by transient absorption. 

It is reasonable to expect that in a viscous monomer such as trimethylol-propane triacrylate (>/ = 65 cp), bimolecular termination reactions proceed more slowly than in monofunctional monomers. However, considering the long lifetime observed for the polymer radicals in these monomers, caution must be exercised in the interpretation of the linear intensity dependence. Long-lived radicals are more likely to terminate by chain transfer and... 

A comparison of the computed results with the experimental data showed that the model predicted the observed trends well. Figure 7 shows the results for one particular level, (7,27). The conclusions from the model were that the intermediate J levels were, in fact, stable and that the shortening of lifetime observed in the 50—200mTorr helium pressure region was due to upward R—T transfer which takes excited molecules out of the initially formed stable state into one which is unstable because of predissociation. The onset of predissociation was predicted to occur in J — 28 1. In a later study [43] using a different apparatus where the pressure could be reduced to less than 1 mTorr, the exact rotational level where predissociation started was confirmed to be J = 28. 

From a theoretical point of view, the ultra-short excited state lifetimes observed for canonical structures have been attributed to the existence of easily accessible conical intersections between the excited state and the ground state efficiently promoting nonradiative decay [10,25, 30, 36,44,45, 53, 58, 60, 74,75, 85, 87, 102], Accurate prediction of excited state properties still presents a major challenge to... 

Under the conditions of their experiment, a zero-pressure lifetime of 0.3 qs was measured for the vibrationally relaxed triplet state at all excitation wavelengths. Since pressures were not low enough to ensure isolated molecule conditions, it is not known from these experiments whether the strong energy dependence of the triplet lifetime observed in other carbonyls will occur in propynal. 

The rate constant for photoinduced electron transfer k4 and the charge recombination rate constant ks are directly observed experimentally. The reciprocal of the 3-ps time constant detected in the transient absorption experiments, equals kn, 3 X 10 s. This assignment is verified by the results for a model P-C6o dyad, where the same value was obtained for the rate constant for photoinduced electron transfer. The charge recombination of (Pzp)3-Pzc-P -C6o is associated with the 1330-ps decay component observed in transient absorption, as demonstrated by the spectral signature of the fullerene radical anion with absorption in the 1000-nm region. This lifetime is within a factor of 2.5 of the lifetime observed for the P" -C6o in a model dyad (480 ps). 

The porphyrin moiety is linked to a benzoquinone derivative which in turn bears a second benzoquinone with better electron accepting properties. Spectroscopic studies revealed that excitation of the porphyrin did indeed lead to the production of a P -Qa Qb state. The lifetime of this state ( 300p in benzene), although longer than that of a related P-Q dyad ( 130ps), was still much shorter than the lifetimes observed for the C-P-Q triad molecules. The reason for this short lifetime probably lies in the conformationally mobile tetramethylene chains which could allow the terminal quinone to fold back toward the porphyrin moiety, and thereby facilitate charge recombination [S9]. 

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