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Structure, Group Theory and Spectroscopic

Let us consider as example PHTh in the anti-coplanar-centrosym-metric structure with the alkyl side chains in the all transplanar conformation and lying in the plane of the Th rinqs. In such a model the translational repeat unit in the 1-d crystal contains two Th rings as in fig. 13 Similar considerations can be made for POTh. [Pg.473]

With such a structure the factor group of the 1-d crystal is isomorphous to the 02 point group. Since N = 50 are the masses in the repeating unit, 3N-4 =146 are the optical q=0 phonons expected in the IR/Raman spectra and 150 are the phonon dispersion branches V(q). The structure of the irreducible representation for q=0 phonons is the following  [Pg.475]

From the above group theory treatment we would expect to observe an extremely complicated spectrum, but in reality the observed spectra are extremely simple. The following theoretical consid- [Pg.475]

V) The normal modes of the side chains in the all-trans structure can be better identified when the band progressions of the q O phonons are considered [5-7]. We expect, in principle, to find the well known and characteristic band progressions for the CH2 wagging-twisting (very weak) (1400-1200 cm ) and CH2 rocking modes (1100-700 cm ) [35]. The band progression of the C-C stretching modes should [Pg.475]

If the anti-coplanar -non centrosymmetric structure of PHTh is considered the point group is and the structure of the irreducible representation is the following  [Pg.475]


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