Platt symbol

Figure 3.13 Pyrene in stretched polyethylene at 77 K. Top baseline corrected polarized absorption spectra Ez(parallel) and Ey (perpendicular to the stretching direction). Centre linear combinations of the polarized spectra Ez and EY. Bottom reduced UV spectra of pyrene. Az= Ez EOEy and AY= 1.75(EY 0.36EZ). Adapted by permission from ref. 182. The Platt symbols l b, La, Bb and Ba labelling the electronic transitions are explained in Section 4.7. The polarization of the weak Lb band shown on the left (<29 000 cm-1, spectra recorded at higher concentration) is of mixed polarization...

The state symbols 1Fb, xLa, lBb and xBa shown in Figure 4.27 were introduced in 1949 by Platt.297,298 He assumed a free-electron model, similar to the electron-in-a-box, in which the 7t-electrons of a cyclic system are confined to a one-dimensional loop of constant potential (a circular wire). The eigenvalues of a single electron in a perimeter of length / are given by Equation 4.37. 

Nous traitons seulement le cas %/s fid lement platt de presentation finie, et k fibres skparees et "sans composante immergee". (Notons que les deux dernieres hypotheses sont des propriety vraies pour un preschema en groupes) Nous allons souvent supprimer le symbols S dans les produits fibres. 

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