  Low-frequency Raman and inelastic neutron scattering of amorphous bis-phenol
A polycarbonate is measured at low temperature, and compared. The vibrational
density of states and light-vibration coupling coefficient are determined. The
frequency dependences of these parameters are explained by propagating
vibration modes up to an energy of about 1 meV, and fracton-like modes in more
cohesive domains at higher energies. The vibrational dynamics is in agreement
with a disorder in the glass, which is principally of bonding or of elasticity
instead of density.
