Serge Richard Minimal escape velocities for unitary evolution groups (232K, PostScript) ABSTRACT. Starting from a strict Mourre inequality, the minimal escape velocity for a unitary evolution group in a Hilbert space is derived under some minimal conditions. If the self-adjoint generator H of this evolution is a Schroedinger operator and if the conjugate operator is the generator of dilations, then it follows that H has very good and easily understandable propagation properties. The striking fact is that no proof of the absence of singularly continuous spectrum of H is available yet under such weak conditions.