Disorder-longitudinal acoustic mode

In addition to longitudinal acoustic modes (section 4.10), the low-frequency regions of Raman spectra often contain rather broad, ill-defined bands. While these can sometimes be ascribed to specific intra- or inter-molecular vibrations, work has suggested they may be due to fracton vibrational modes localised in disordered regions or blobs [241]. Analysis of the bandshape has been used to measure the size of the disordered regions for example, -50A blobs were found in amorphous PET and PMMA [242]. 

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