Distribution of triplets

This is due to the uniform initial condition k(t), which starts from its maximal value ki) Wrrd3r and drops with time, approaching the stationary limit from above. Contrary to this famous result, the experimental study of delayed fluorescence of anthracene in viscous solution [262] showed quite the opposite time behavior of k t). As it is initially much less than ko, the rate constant increases with time, approaching the long-time asymptote (3.56) from below. The authors of Ref. 262 called this anomaly the anti-Smoluchowski time behavior of the delayed fluorescence. They properly attributed it to a nonuniform distribution of triplets generated by the intersystem conversion from singlets that are preliminary quenched by the resonant energy transfer. 

The MET employed in Ref. 264 allows us to find the distribution of triplets at the end of a long pulse, which accounts for their static annihilation ... 

Rothe C, Monkman A (2002) Dynamics and trap-depth distribution of triplet excited states in thin films of the light-emitting polymer poly(9,9-di(ethylhexyl)fluorene). Phys Rev B 65(7) 073201... 

The effect of the partial alignment on the intensity distribution of triplet esr-spectra is shown in Fig. 10b for naphthalene as guest. Spectra are shown for an mentation of the liquid crystal tic axis L either perpendicular (upper trace ... 

The long triplet lifetimes are attributed to reversible triplet energy transfer with the appended pyrene moieties and, using ultrafast transient absorption spectroscopy, the rates of formation of the equilibrium distribution of triplet states were determined [188]. 

The EPR spectrum of the ethyl radical presented in Fig. 12.2b is readily interpreted, and the results are relevant to the distribution of unpaired electron density in the molecule. The 12-line spectrum is a triplet of quartets resulting from unequal coupling of the electron spin to the a and P protons. The two coupling constants are = 22.38 G and Op — 26.87 G and imply extensive delocalization of spin density through the a bonds Note that EPR spectra, unlike NMR and IR spectra, are displayed as the derivative of absorption rather than as absorption. 

Consider now an encounter (F) radical pair formed from two free radicals. Since there are three components to the triplet state, T+i, To and T j, and only one singlet component, S, the encounter of two free radicals having uncorrelated spins leads to a statistical distribution of T and S radical pairs. However, some of the S radical pairs will react without undergoing T-S mixing, and this has the effect of increasing the relative number of T radical pairs. Consequently the F-pairs will give the sam e type of polarization as the T-pairs, but the degree of polarization will be less. 

A different situation arises with a preliminary reduced surface. In this case the measured value of y is within lO - 10 2, and as the temperature increases, the y grows by the Arrhenius Law (Equation) with the activation energy of 5.2 kcal/mole. In addition, there is dependence of y upon the triplet oxygen pressure in the set-up, though the experiment conditions allow us to neglect a priori the impact of homogeneous processes on the spatial distribution of 02( A ) molecules. Prolonged... 

The bimodal velocity distribution of the 0(3Pj) fragments produced via the triplet channel in the UV photodissociation of ozone has also been observed by Syage41,43>46 and Stranges et al.AA at photolysis wavelengths of 226 and 193 nm, respectively. Both authors measured anisotropy parameters for the fast and slow product pathways separately. 

Fig. 5. Electron-impact efficiency curves at (a) m/e = 41 and m/e = 13, and (b) m/e = 14, recorded at a lab angle of 30° during the CMB study of the reaction 0(3P) + C2H2 at Ec = 12.6kcalmol 1. The thick arrow marks the electron energy (17eV) used for product angular and TOF distribution measurements. In (b) the thin arrow marks the literature value50 of the IE of triplet methylene (see text).

Fig. 11. Center-of-mass translational energy distribution of the CH2 + H product channel of CH3 photodissociation at 193 nm. Arrows indicate the thermodynamic maximum available energies for formation of singlet and triplet methylene. (From North et al.112)...

Thus the triplet states of the two diastereomers react to yield different product distributions although this effect is far less marked for the triplet than for the singlet reaction, which is essentially stereospecific. The singlet reaction could be either concerted or due to an extremely shortlived biradical. Since the product distributions of the triple reaction of these two diastereomers are different, it is clear that cleavage must occur before complete equilibration. Thus the lifetime of the aliphatic ketone derived biradical must be considerably shorter than the corresponding biradical derived from an aryl ketone. 

The relative reactivity of cyclopentadiene and ds-dichloroethylene toward triplet cyclopentadiene was found to be greater than 20 1 while that for cyclopentadiene and trans-dichloroethylene is less than 5 1. Thus the trans isomer is about four times more reactive toward the triplet cyclopentadiene than the cis isomer. An interesting temperature dependence of the product distribution of this reaction has been reported (Table 10.8). The data in Table 10.8 indicate that the relative amount of 1,4 addition [products (39) and (40)] is much more sensitive to temperature than 1,2 addition [products (35)—(38)], especially for the trans-olefin. The data also indicate that some rotation about the CHC1-CHC1 bond occurs in intermediate radicals derived from both cis- and trans-dichloroethylene. However, rotational equilibrium is not established at ring closure since the ratios of ds-dichlorocyclobutanes... 

In addition, it was observed that the sensitized photolysis produced the same distribution of products with the same efficiency (fingerprint characteristic of the triplet state). From quenching studies the specific rate constant for the rearrangement could be obtained. Phenyl migration rearrangement is of intermediate efficiency, interposed between the more efficient and less efficient type A processes (Table 7.4). The type of mechanism proposed for this transformation is as follows ... 

Abstract. We present metallicities for 487 red giants in the Carina dwarf spheroidal (dSph) galaxy that were obtained from FLAMES low-resolution Ca triplet (CaT) spectroscopy. We find a mean [Fe/H] of —1.91dex with an intrinsic dispersion of 0.25 dex, whereas the full spread in metallicities is at least one dex. The analysis of the radial distribution of metallicities reveals that an excess of metal poor stars resides in a region of larger axis distances. These results can constrain evolutionary models and are discussed in the context of chemical evolution in the Carina dSph. 

Temperature changes could also have another effect. Steroidal ketones have been demonstrated to have nearly degenerate zn-n and states, and the possibility of a thermal equilibrium between those states has been pointed out. 146> In fact, testosterone acetate and 10-methyl-A -oct alone, both very similar molecules to the reactant in Eq. 55, undergo photoreactions from two different triplet states. 144> So we ought to consider what the reactivity of the n-n state would be, and whether product distribution would differ from the two states. If so, temperature variation could change product distribution due to a change in the relative proportions of triplet states. 

Figure 2.44 (afi) Two different and isosteric orientations of triplets of trails planar chains of sPS as in structure of a-form (Figure 2.24). (c) Atoms of backbone are statistically distributed in six positions around threefold axis, whereas atoms of phenyl rings are in same positions as in... 

Besides a poorly resolved triplet structure in the EPR spectrum of 57Fe enriched two-iron ferredoxins266 at gz, no hf interactions are observed in all these iron-sulfur clusters. The distribution of principal axes of the g tensors gives rise to an inhomogeneous, field-dependent EPR linewidth, and obscures the resolution of ligand hfs265. This distribution, whose origin is not completely established, does not, however, prevent application of the ENDOR technique. 

The structure of a liquid is conventionally described by the set of distributions of relative separations of atom pairs, atom triplets, etc. The fundamental basis for X-ray and neutron diffraction studies of liquids is the observation that in the absence of multiple scattering the diffraction pattern is completely determined by the pair distribution function. 

Fig. 19.8 Distribution of electronic charge in graphene cluster C65H20. (The details for the quintet are shown and only the essential information for the two triplets.)...

Equation (4) describes a partition between two forms of the complex one, with fraction f, that exhibits quenching and one that does not. Equation (5) corresponds to a distribution of forms with a range of quenching rates whose breadth varies inversely with n the occurrence of distributions is well-established for proteins at low temperatures [29]. In either case, the non-exponential kinbtics necessitate that conformational interconversion in the transition range is slow compared to the lifetime of the triplet state and the gating limit is applicable. 

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