The inelastic scattering of 164 MeV pions from ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ is studied using the distorted-wave impulse approximation in momentum space. The sensitivity of the predictions to various shell model descriptions of the yrast $2^{+}$ state is examined in detail. The excitation of the triplet of states ($4_1^{+}$, $0_2^{+}$, $2_2^{+}$) near 3.7 MeV and the ($3_1^{-}$, $0_3^{+}$, $0_3^{+}$, $2_3^{+}$) triplet at about 5.2 MeV are also investigated within the context of the shell model. In order to explain the scattering to natural parity states [those with angular momentum $J$ and parity ${\mathrm{}(-1\mathrm{})\mathrm{}}^J$], one must enhance the theoretical results by about the same factor as needed to explain the $B\left(\mathrm{EJ}\right);0\mathrm{}\to J$ transition rates obtained from electromagnetic excitation. The sensitivity of the results to the isoscalar or isovector character of this enhancement is examined. Agreement between distorted-wave impulse approximation calculations and experiment is found to be satisfactory.

NUCLEAR REACTIONS, NUCLEAR STRUCTURE ($\pi ,{\pi }^{\prime }$) $E_{\pi }\approx 164$ MeV; ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ target, theoretical $\frac{d\sigma }{d\Omega }$ based on DWIA in momentum space; effects of different shell model descriptions studied.

• Received 28 September 1979

DOI:https://doi.org/10.1103/PhysRevC.21.679