[en] The structure of β'-MoO₃, a new modification of MoO₃, is closely related to the structure of ReO₃ and has been refined using high resolution neutron powder diffraction data and the Rietveld technique. The structure is monoclinic (P2₁/n, a = 7.415(1), b= 7.433(1), c = 7.654(1), A, β = 90.09(2)). β'-MoO₃ is isostructural with the room temperature monoclinic modification of WO₃ and may be derived from the deuterated intercalate (D_xMoO₃), also with ReO₃-type structure, by heating in oxygen at 200 degrees C. The modification is structurally intermediate between the WO₃-type and the thermodynamically stable α-MoO₃. (author) 9 refs., 2 figs., 2 tabs