  We measured dispersive spin excitations in $\mathrm{SmFeAsO}$, parent
compound of $\mathrm{SmFeAsO_{\text{1-x}}F_{\text{x}}}$ one of the highest
temperature superconductors of Fe pnictides (T$_{\text{C}}\approx$55~K). We
determine the magnetic excitations to disperse with a bandwidth energy of ca
170 meV at (0.47, 0) and (0.34, 0.34), which merges into the elastic line
approaching the $\Gamma$ point. Comparing our results with other parent Fe
pnictides, we show the importance of structural parameters for the magnetic
excitation spectrum, with small modifications of the tetrahedron angles and As
height strongly affecting the magnetism.
