Low-frequency Raman scattering experiments have been performed on metal nan
oparticles embedded in two different thermally treated matrices. In additio
n to the well-known Raman scattering by the nanoparticle quadrupolar vibrat
ional mode, the spectra measured in the 3-40 cm(-1) frequency range exhibit
several new bands. They are ascribed to resonant scattering by the nanopar
ticle breathing mode and its harmonics, in very good agreement with time-re
solved measurements. (C) 2001 American Institute of Physics.