We report the polarized Raman spectra of undoped $R\mathrm{FeAsO}$ ($R$=Sm, La) collected at room temperature from $ab$ surfaces of impurity-free microcrystals. The spectra exhibit sharp phonon lines on very weak electronic scattering background. The frequency and symmetry of the four Raman phonons involving out-of-plane atomic vibrations are found at $170{\mathrm{cm}}^{-1}$ ($A_{1g}$, Sm), $201{\mathrm{cm}}^{-1}$ ($A_{1g}$, As), $208{\mathrm{cm}}^{-1}$ ($B_{1g}$, Fe), and $345{\mathrm{cm}}^{-1}$ ($B_{1g}$, O) for $\mathrm{SmFeAsO}$; and $162{\mathrm{cm}}^{-1}$ ($A_{1g}$, La), $208{\mathrm{cm}}^{-1}$ ($A_{1g}$, As), $201{\mathrm{cm}}^{-1}$ ($B_{1g}$, Fe), and $316{\mathrm{cm}}^{-1}$ ($B_{1g}$, O) for $\mathrm{LaFeAsO}$.

• Received 15 April 2008

DOI:https://doi.org/10.1103/PhysRevB.77.220505