Modern Polymer Spect..

136 3 Vilwtrtionrrl Spectra (1s N Probe of Striictiirul Orrlev
I
/I/
11 c)
‘1 ‘1 w=2729.5 cm-l
di
I“ w=270u.5 cm-l
el
Figure 3-21. Sample eigenvectors
in the HC1 stretching region for a
single chain of mixed 25% DCI in
HC1. The top line gives the distribution
of defects. Vibrational displacements
are rotated of 90” for
motions.
changes. The vectorial sum of the dipole moment changes is related to the absorption
intensities. We can then qualitatively predict also the intensity of each of the
calculated modes. The distribution of defects given at the top of the figure indicates
the existence in the chain of 14 DCl isolated units (Z = l), 14 doublets (Z = 8) +1
triplet (Z = 3). Application of NET, IIM, and intensity coinsiderations indicate that
at 1’ = 1948.76 cn-l only the single DCl niolecules as isolated entities perforin fully
localized vibrations at the site where they are located with strong intensity. At
v = 1948.5 and 1948.68 cni-’, the four single units separated only by one HCl
spacer feel some intramolecular coupling and generate localized modes with some
phase coupling, the former has strong intensity and the latter zero intensity. Next,
at 1’ = 1941.5 cm-’ only isolated doublets generate an in-phase motion (strong) of
the two molecules. The out-of-phase motion occurs at Y = 1956.5 cm-] (inactive).
Finally, the motions characteristic of the triplet occur at 1’ = 1938.5 (strong) and
1959.9 cn1-l (weak). It is also apparent that in this frequency range the atoms which
belong to the host lattice do not move (i.e., the motion of the DC1 defect is not
propagated throughout the chain of the host HCl lattice). The concept we wish to
stress here is that the cases just examined are typical examples of modes localized in
space and energy characteristic of particular ‘defects’ or of ‘islands’ or ‘clusters’ of
defects. Moving to the HCl stretching range (near 2700 cm-I) the analysis of the
composition of the chain from localized modes can be completed. For the same
chain considered in Figure 3-22 the distribution of HC1 sequences is the following:
4 (Z = I), 4 (Z = 2), 3 (Z = 3), 2 (Z = 4), 2 (Z = 5), 2 (Z = 6), 1 (Z = 7), 1 (Z = 8)
and 1 (Z = 9). From Figure 3-22, the ‘island analysis’ carried out using the IIM
method allows the following frequencies Characteristic of each island to be located