  We demonstrate the determination of anharmonic acoustic phonon properties via
second-order Raman scattering exemplarily on copper iodide single crystals. The
origin of multi-phonon features from the second-order Raman spectra was
assigned by the support of the calculated 2-phonon density of states. In this
way, the temperature dependence of acoustic phonons was determined down to
10\,K. To determine independently the harmonic contributions of respective
acoustic phonons, density functional theory (DFT) in quasi-harmonic
approximation was used. Finally, the anharmonic contributions were determined.
The results are in agreement with earlier publications and extend CuI's
determined acoustic phonon properties to lower temperatures with higher
accuracy. This approach demonstrates that it is possible to characterize the
acoustic anharmonicities via Raman scattering down to zero-temperature
renormalization constants of at least 0.1\,cm$^{-1}$.
