[en] A quantum model, consisting of a rotating harmonic oscillator, has been developed for the neutron scattering cross section of a homonuclear diatomic molecule. The translationaldynamics of the molecular centers of mass is also accounted for. The model is developed in particular for the case of the integral neutron cross section of the hydrogen isotopes. It is shown that, to the lowest-order approximation, the picture reduces to that of a rigid-rotor model modulated by a Debye-Waller factor. However, the accurate results shows a nonnegligible correction that should be taken into account if a proper analysis of the experimental diffraction data is to be performed. (orig.)