The fourth $2^{+}$ state in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ at an excitation energy of 8.21 MeV has been studied by high-resolution electron scattering. The Coulomb form factor for this state was measured in the momentum-transfer range 0.9≤q≤2.1 ${\mathrm{fm}}^{\mathrm{-}1}$ and the extracted B(C2)↑ value was determined to be 7.3±4.2 $e^2$${\mathrm{fm}}^4$. The level at 8.21 MeV is identified as a four-particle, two-hole (4p2h) state of the type $p^{\mathrm{-}2}$(sd${)}^4$. Form-factor measurements in the range 1.0≤q≤1.9 ${\mathrm{fm}}^{\mathrm{-}1}$ are also presented for a strongly excited normal-parity state at 9.36 MeV. Preliminary measurements of the differential cross section for exciting this state by 135-MeV protons suggest a $2^{+}$ assignment; the measured Coulomb form factor of this state allows it to be identified as the best experimental candidate for a predicted K=2 4p2h state with the four sd-shell nucleons coupled to T=0. The excitation of these states and other members of rotational bands in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ are discussed within the framework of structure models. Shell-model calculations for the C4 form factors of the first three $4^{+}$ states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ are compared to existing data.

• Received 18 September 1989

DOI:https://doi.org/10.1103/PhysRevC.41.448