Coexistence of Single-Particle, Collective-Quadrupole, and $\alpha$+${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ Molecular-Dipole Degrees of Freedom in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$

All natural-parity states of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ have been studied with high accuracy with the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}({}_{}{}^7{}_{}{}^{}\mathrm{Li}, t\gamma ){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ coincidence and ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(\alpha , \gamma ){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ radiative-capture reactions. The four-particle, two-hole $0_2^{+}$, $1^{-}$, $2_3^{+}$, and $3_3^{-}$ states deexcite with consecutive enhanced $E1\mathrm{}$ and $E2\mathrm{}$ cross-over transitions having $B\left(E1\mathrm{}\right)\mathrm{}\simeq {10}^{-2\mathrm{}}$ Weisskopf units (W.u.) and $B\left(E2\mathrm{}\right)\mathrm{}\simeq 20$ W.u. These data suggest the existence of an $\alpha$ +${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ dipole band in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ similar to those discussed recently by Iachello and Jackson.