  We measured the Raman and the Infrared phonon spectrum of SmFeAsO
polycrystalline samples. We also performed Density Functional Theory
calculations within the pseudopotential approximation to obtain the structural
and dynamical lattice properties of both the SmFeAsO and the prototype LaFeAsO
compounds. The measured Raman and Infrared phonon frequencies are well
predicted by the optical phonon frequencies computed at the Gamma point,
showing the capability of the employed ab-initio methods to describe the
dynamical properties of these materials. A comparison among the phonon
frequencies of different oxypnictides suggests a possible role of the high
frequency phonons in the pairing mechanism leading to superconductivity in
these materials.
