Regge poles describing shape resonances ("quasimolecular states") are found to play a prominent role in many optical-model scattering amplitudes and appear to be directly related to the Gruhn-Wall "dip" often observed in the reflection coefficient $\eta \mathrm{}\left(l\right)\mathrm{}$. The Blair smooth-cutoff model is generalized to include such a Regge pole and used to fit angular distributions for elastic ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+ ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and $\alpha +{}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ scattering, in the 20-30-MeV (c.m.) energy range. It also appears that the smooth-cutoff (strong-absorption) model itself can be interpreted as the result of many overlapping inelastic Regge resonances.

• Received 28 October 1970

DOI:https://doi.org/10.1103/PhysRevC.3.1104