[en] In an inelastic neutron experiment on RbAg₄I₅ a broad quasielastic peak was observed throughout Q-space. As the temperature was lowered, the quasielastic peak became a broad propagating excitation with dirac constant ω approx. 2.2 meV. This excitation was measured along several symmetry directions and it exhibited little dispersion. This confirms that the original idea of a single particle excitation corresponding to the Ag⁺ ions moving within a potential well created by the rest of the lattice. The temperature dependence of this excitation is consistent with recent calculations of neutron scattering in superionic conductors