We report the inelastic light scattering studies on SmFeAsO0.65 and SmFeAsO0.77H0.12 with iron isotopes namely 54Fe and 57Fe. In both of these systems under investigation we observed a significant shift in the frequency of the phonon modes associated with the displacement of Fe atoms around ~ 200 cm-1. The observed shift in the Fe mode (B1g) for SmFeAsO0.65 is ~ 1.4 % and lower in case of SmFeAsO0.77H0.12, which is ~ 0.65 %, attributed to the lower percentage of isotopic substitution in case of SmFeAsO0.77H0.12. Our study reveals the significant iron isotope effect in these systems hinting towards the crucial role of electron-phonon coupling in the pairing mechanism of iron based superconductors.
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