Symmetric properties levels

Eastman s pioneering work has already been reviewed their approach involved introduction of aromatic monomers into aliphatic-aromatic polyesters such as PET. The increased symmetric ring content Imparts melt anisotropy to the copolyester but, as mentioned, the aliphatic-aromatic structure has not given the mechanical property levels noted for the wholly aromatic polyesters. 

From the selection rules of the 6j coefficients (.89), it follows that the biquadratic terms cannot mix the S = I levels with higher spin states. By contrast, the anisotropic symmetric and antisymmetric terms, whose magnitude is related to that of the isotropic component (89), can give rise to a substantial mixing. However, a detailed quantitative model is needed to verify whether the peculiar magnetic properties of [3Fe-4S] + centers can be explained by this mixing. 

In fact, the barrier for proton transfer in the maleate anion appears to lie below the zero-point vibrational energy level (W. M. Westler, private communication). Thus, vibrationally averaged properties of the maleate anion will correspond to a symmetrically bridged Cjv transition-state structure rather than to either of the asymmetrically bridged equilibrium structures in Fig. 5.22. For present purposes this interesting feature of the potential surface can be ignored. 

Disulphonated dyes of Mr 800-1000, many of them symmetrical in structure. Although often cheaper to manufacture than the unsymmetrical monosulphonates and the unsulphonated types, these slow-diffusing complexes have intrinsically poor levelling and migration properties. 

The structures of the neutron-rich isotopes 97Y, 98Y and 99Y reflect with special clearness the rapid change of the nuclear shape at neutron number 60. The discovery of a new isomer in 97Y has provided evidence for the shell-model character of this nucleus even at high excitation energies while 99Y shows the properties of a symmetric rotor already in the ground state. The level pattern of the intermediate isotope 98Y indicates shape coexistence. 

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