Properties of the E1 giant resonance built on the first excited state of 16O.

Abstract

Radiative capture of protons leading to the first excited state of $^{16}\mathrm{O}$ (${E}_{x}$=6.05 MeV, ${J}^{\ensuremath{\pi}}$${=0}^{+}$) has been measured in the energy range ${E}_{\mathrm{p}=10\char21{}}$17 MeV in 200 keV steps. A pronounced concentration of dipole strength is observed, which is interpreted as a giant dipole resonance built on the ${0}_{2}^{+}$ state. The observed strength has a \ensuremath{\gamma}-ray energy significantly less than that for the giant dipole resonance built on the ground state. The sign and magnitude of the shift is what would be expected if the giant dipole resonance observed is the lower energy component of a resonance split because of interaction with the quadrupole deformation of the ${0}_{2}^{+}$ state, although this conclusion is model dependent. The strength of the excited state giant dipole resonance is somewhat larger than would be predicted by simple models in which the strength scales with the proton spectroscopic factor of the final state.