Modern Polymer Spect..

188 3 Vibrational Spectra as a Probe ojStrticttirci1 Order
ORTH.
MELT
I , 1 I
2wQ 2800 ” 1200 800 coo 0
v cm-1
I
Figure 3-51. Changes of the Raman spectrum of n-nonadecane in the various phases: (a) ortliorhombic,
(b) a, (c) liquid.
The Raman spectrum in the melt shows the following features:
(t) At Tm the LAM1 mode disappears completely and is replaced by the so-called
‘pseudo LAM’, a broad and weak scattering near 320 cn1-l common to all
liquid n-alkanes, melt polyethylene or any molecule containing long CH2
chains in the ‘melt’ state (Figure 3-51c).
(u) At T, the Raman lines at 866 and 844 cm-’ gain in intensity and, together
with the line near 890 cm-l, form a strong characteristic triplet with components
of similar intensity (Figure 3-51c).
(v) At Tm the Fermi resonance line at 1461 cmP1 decreases while the Fermi resonance
line at 2930 cm-‘ increases.