Proton spin flip in the excitation of the first $2^{+}$ states in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$ has been measured at 30 MeV using the ($p,p^{\prime }\gamma$) coincidence technique. The data are fit by the distorted-wave Born-approximation (DWBA) collective model using the full Thomas spin-orbit coupling term and the DWBA microscopic model using a real interaction. The effect of adding an imaginary part to the microscopic interaction was investigated with respect to the present spin-flip data and published asymmetry data. It is concluded that such a term can be important.

• Received 15 September 1971

DOI:https://doi.org/10.1103/PhysRevC.5.561