Anharmonic effects in crystals typically result in the symmetric broad
ening of the single-phonon Lorentzian line shape. However, a simple mo
del, based on consideration of a highly anharmonic potential, shows th
at anharmonicity can lead not only to asymmetric line shapes but also
to line shapes composed of multiple subpeaks. Experimental Raman data
on the soft A1(TO) phonon in ferroelectric PbTiO3 indicates that this
mode does indeed consist of a series of subpeaks whose intensities are
accurately predicted (with no fitting parameters) by our model.