Nucleon momentum distribution in colliding nuclei and potential between excited nuclei studied with the Vlasov equation

The momentum distribution of nucleons in colliding ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$${+}^{16}$O system is studied with the Vlasov equation in the incident energy region of 20–100 MeV/nucleon. A shift of the momentum distribution to higher momenta is observed until the time of full overlap of two nuclei. It is attributed to the acceleration of the colliding nuclei, and discussed in terms of the newly defined potentials acting between two excited nuclei. The acceleration of colliding excited nuclei is even larger than that in the elastic channel at 40–100 MeV/nucleon. This is due to the dynamical change of the density distribution avoiding high density.