Validity of the Adiabatic Cranking Model when Applied to Fission

The cranking model is applied to a two-center, asymmetric, shell model plus a pairing interaction. The energy increase due to the enforced collective motion is determined up to fourth order in the collective velocity. For a motion across the second saddle of ${}_{}{}^{236}{}_{}{}^{}\mathrm{U}$ the higher order terms are so large that the validity of the adiabatic model as a first approximation to fission dynamics is questionable.