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The temperature dependences of the first moments of phonon Raman scattering lines are studied for Fe1-xZnxF2. The diamagnetic dilution diminishes the spin-phonon coupling strength of phonons with both A1g and Eg symmetry in proportion to the decrease in the ordering temperature TN. Moreover, the Eg mode shows an asymmetrical lineshape for Zn concentrations x>0.3. It is explained by an unresolved superposition of two modes, one of which is ascribed to perturbed ZnF2 with broken translational symmetry.