Quadrupole excitations in the nucleus ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$ have been studied in a semiclassical framework using the nuclear Vlasov equation solved with the test particle method. A soft mode of quadrupole excitation located around 2 MeV is found. The strength (in percentage of the energy-weighted sum rule) exhausted in such a soft quadrupole excitation region is very sensitive to the extension of the neutron halo in the nucleus ${}_{}{}^{11}{}_{}{}^{}\mathrm{Li}$. The results are discussed in comparison with other recent calculations. The use of the collective response to tune phase-space models of neutron excess nuclei to be used in collision dynamics is finally stressed.

• Received 4 August 1994

DOI:https://doi.org/10.1103/PhysRevC.50.2809