Four-Nucleon Transfer fromO16toZr90near the Coulomb Barrier

The transfer of two neutrons and two protons is found to be the dominant reaction process in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$+${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ near the Coulomb barrier. The reaction was identified from $\gamma$-ray spectra measured in coincidence with backward-angle charged particles. A band of excited states in the residual nucleus is found to be selectively populated. The energy dependence of the centroid energy of this band is studied and compared with theories of sub-Coulomb transfer reactions.