  We study diffractive scattering cross sections, focusing on the rapidity gap
distribution in realistic kinematics at future electron-ion colliders. Our
study consists in numerical solutions of the QCD evolution equations in both
fixed and running coupling frameworks. The fixed and the running coupling
equations are shown to lead to different shapes for the rapidity gap
distribution. The obtained distribution when the coupling is fixed exhibits a
shape characteristic of a recently developed model for diffractive
dissociation, which indicates the relevance of the study of that diffractive
observable for the partonic-level understanding of diffraction.
