Modern Polymer Spect..

3 I1 A Yey) Siiiiple Case: LLittice Dynnniics of HCl-DCl Mixed Cvvstu1,s 133
Figure 3-18 (b)
b
Suitable experimental procedures were envisaged in order to obtain such materials
and in order to record the infrared spectra to be compared with the calculated
ones.
Figure 3-18a immediately indicates that the HC1 stretching of molecules isolated
in a DCl lattice can generate localized out-of-band modes, while DCl stretching in
a HCl host lattice generate typical localized gap-modes. This can occur for other
lower-frequency modes for both molecules. The 03-co4 branches span frequency
ranges with partial overlapping between HCl and DCI lattices, thus possibly generating
resonance modes. Also, the vibrations of 07-Wg may couple. No coupling
can occur between the out-of plane phonons of HC1 (05-06) and the in-plane
phonons of DC1 (w3-014) since they are orthogonal.
The histograms calculated for the three isotopically impure chains are given in
Figure 3-19 and show a complicated and almost inextricable pattern. Some details
are enlarged in Figure 3-20.