A multistep $\alpha$-particle-transfer picture is used to describe anomalous back-angle elastic scattering of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$. Transfer of two and three $\alpha$ particles is described in a semiclassical treatment of the interplay between absorption and transfer processes. The energy dependence of the anomalous contribution to the elastic $S$ matrix due to these processes is estimated and shown to be consistent with the overall trend of the data.

• Received 17 May 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.95