Elastic and inelastic scattering of 120 MeV 18O from 208Pb and the spin alignment of the 2+ state of 18O

The elastic and inelastic scattering of 18 O ions at 120 MeV from a target of 208 Pb have been studied. Cross sections for excitation of the 2 + state at 1.982 MeV in 18 O and of the 3 − state at 2.61 MeV in 208 Pb were measured. In addition, the populations of the m -substates for the 18 O excitation were deduced from the Doppler-broadened line shapes. The data were subjected to a coupled-channels analysis using either Woods-Saxon or folding-model potentials. In addition, the 18 O excitation was found to be described very well by use of a semi-microscopic model. The analyses consistently indicated the presence of a positive static hexadecapole moment of several e · fm 4 for the 2 + state of 18 O. The m -substate population distributions were found to be better fitted if a vector spin-orbit coupling was introduced for the 2 + state of 18 O with a sign opposite to that for the nucleon-nucleus case.