Epsilon value

The MWBD method also requires an independent measure of the branching structure factor e. For our analysfs of polyvinyl acetate, it was obtained by comparing M and Bf values calculated from SEC data, analyz d using the MWBD method and various epsilons, and the Mfj and Bj values predicted by Graessley s (21) kinetic model. An epsilon value of 1.0 was found to fit best. 

We have seen from the above work that the nonradiative rate constants dominate the luminescence behavior of ruthenium(II) complexes. If one can increase the value of the radiative rate constant, kr, without substantial increases in knr, then emission efficiency can be improved. The radiative rate constant is, in theory at least, related to the molar absorption coefficient, epsilon187. Demas and Crosby188, made a number of assumptions and calculated radiative lifetimes based on observed epsilon values, which were in good agreement with the experimental kr values. Watts and Crosby1895 went on to comment on the possible implications of the epsilon value. 

One final series of quinoline-based ligand complexes (in which there is no steric effect) has been found to be rather unusual248,251,252. The ligand i-bq is expected to behave as a substituted bpy. [Ru(i-bq)3]2+ has a potential (III/II) of 1.12 v indicating less stabilization of ruthenium(II) than in [Ru(bpy)3]2+ 252). The epsilon value is nearly twice that of [Ru(bpy)3]2+, suggesting that the compound should be an efficient emitter. It turns out that in this complex an entirely different luminescence mechanism is operative. [Ru(i-bq)3]2+ shows ligand-centered luminescence, which is unusual in a ruthenium com-... 

At present, several factors can be seen as being important in the emission efficiency -molecular structure relationship. The extent of conjugation appears to be one which has been little examined so far. To some degree, the molar epsilon value is a measure of extent of conjugation and appears to have some relationship to efficiency. From energy... 

Although K may be a better analogue for NH4 than Na, the values for Na were used because a consistent set of concentration independent and dependent epsilon values (si and S2) are available only for (Na - ) interactions. The si and S2 values for other K2L and Na2L interactions are very small in... 

For cases where the uncertainties in the epsilon values collected in Table B-4 and Table B-5 are +0.03 kg-mof or greater, Ciavatta [1980CIA] proposed the use of Equation (B.3)... 

Thus the optimised value is not significantly different from the value based on the mean epsilon values, but the uncertainty is slightly larger. The value including the uncertainty in the epsilon values would translate into log, K° (D.l) = (10.748 + 0.053) for Reaction (D.l) as compared to log, AT°(D.l) = (10.748 + 0.038) based only on the mean epsilon values (Table IX-6). 

The data can be used to test whether the UV transient is spectrally similar to the dibromide ion-radical in the course of its decay by converting fi to k(2) by multiplying it at each wavelength by the epsilon values for the fir2 radical, as shown in the last column of Table IV. For both air- and N20-saturated samples, the constancy of these k(2) values again shows the spectral similarity of the seawater transient to the dibromide ion-radical. The absolute values of k(2) in air- and N2-saturated samples are in reasonable agreement with those expected (Fig. 2) the imperfect agreement probably reflects the poorer constraints on k(2) in the presence of a substantial a term. Possibly there is a real difference between the two conditions. However, this supposed spectral difference is not reflected in the interpretationally more important exponential decay terms. 

The slope of the best-fit line proportional to an age of 3.54 0.03 Ga the intercept of this line on the Nd/ Nd a3ds where Sm/ Nd - 0 is the initial Nd/ Nd ratio and is 0.50809 0.00004. The epsilon value (e j +L16) is a measure of the difference between the initial ratio and a chondritic model for the Earth s mantle at 3.54 Ca expressed in parts per 10 000 (see Section 6.3.4 and Box 6.2). The positive value for epsilon indicates thar the volcanic ro< were derived from a (slightly) depleted mantle source at 3.54 Ga, although there are large errors on this estimate. 

Table 6.8 Parameters used in the calculation of model ages and epsilon values for strontium isotopes...

Othman et al. (1984), reduces to an epsilon value of +2.5 at 4.0 Ga. Some support for depleted mantle very early in the history of the earth comes from the work of CoUerson et aL (1991). 

Calculating In the study of neodymium isotopes the epsilon parameter is a measure of the epsilon values difTerence. between the Nd/ Nd ratio of a sample or suite of samples and a reference value, which in this case is CHUEL Epsilon values are used in three slightly different ways (see the worked examples in Box 6.2) which are described below. 

CaJ Epsilon values calculated for an isochron Epsilon values are frequently quoted for Sm Nd isochrons and are a measure of the difference between the initial ratio of the sample suite and CHUR at the time of formation, expressed in parts per 10 (see Figure 6.2). They are calculated from the expression... 

Epsilon values Epsilon values may be calculated from Sr/ Sr ratios in exactly the same way... 

This value may then be compared with CHUR to calculate the epsilon value using the equation... 

Epsilon values (today) for individual samples are a measure of the extent to which the individual samples are fractionated relative to CHUR as defined by the fractionation factor (see below and Figure 6.19). 

Epsilon values vary with time and the following approximation may be used to calculate epsilon (f) from epsilon (today) ... 

Time (r)- epsilon evoludon diagram for 3.8 Ga metakomadites from Labrador (adapted from CoUerson et aL, 1991). Komadites were produced from depleted mantle at 3.8 Ga with individual samples ranging in composidon from E = H-0.2 to +2.3, and with variable Sm/Nd rados q 0.S9). Individual samples have evolved to present-day epsilon values... 

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