  Hydrostatic pressure Raman measurements have been carried out on the SmFeAsO
series of oxypnictides with varying amount of doping (F substitution for O and
Co for Fe) and transition temperature (T_{c}), in order to investigate lattice
modifications and their connection to doping and superconductivity. Synchrotron
XRD data on some of these compounds indicated that at low doping the lattice
constants vary smoothly with pressure, but with increasing F concentration
there is a deviation from the normal equation of state and these effects are
related with modifications in the superconducting FeAs4 tetrahedra. The
hydrostatic pressure Raman measurements show that the A1g mode of the rare
earth atom for the superconducting compounds deviates from the linear pressure
dependence at the same pressures where the XRD results indicate
pressure-induced lattice anomalies. A similar anomaly is found for the As
phonon of same symmetry. As in cuprates, the effect is diminished in the
undoped compounds and it is not related with the F substitution being present
in the Sm(Fe_{1-x}Co_{x})AsO as well. The calculated Gr\"uneisen parameter for
the Sm phonon ({\gamma \approx}1.5) is very similar to the corresponding values
of cuprates and it does not vary with doping. For the Fe mode it has higher
value ({\gamma \approx}1.8) than for As ({\gamma \approx}1) indicating a more
anharmonic phonon.
