Recently measured gross structure in the 180° excitation function of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ + ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ elastic scattering is fitted very well by including a small parity-dependent term in an energy-dependent and surface-transparent optical potential. This interpretation is in contrast to a previous proposal suggesting that the structure is due to potential shape resonances of varying principal quantum numbers $n$ and angular momenta $L$.

• Received 20 April 1978

DOI:https://doi.org/10.1103/PhysRevLett.40.1549