Low-lying E 1 strength in 20 O

Intermediate energy Coulomb excitation at 100 MeV/nucleon was used to probe the low-lying level structure of both ${}^{18}\mathrm{O}$ and ${}^{20}\mathrm{O}$ in the region between 1 and 8 MeV. Discrete ${1}^{\ensuremath{-}}$ states with energies of 5.35(10) and 6.85(5) MeV were observed in ${}^{20}\mathrm{O}.$ The strong direct excitation and subsequent $\ensuremath{\gamma}$-ray decay of these states, along with $B(E\ensuremath{\lambda})$ predictions for ${}^{18,20}\mathrm{O}$ levels in this energy region, established their dipole character. The extracted $B(E1)\ensuremath{\uparrow}$ values of ${0.062(16)e}^{2}{\mathrm{fm}}^{2}$ and ${0.035(9)e}^{2}{\mathrm{fm}}^{2}$ for the 5.35- and 6.85-MeV states, respectively, are significantly larger than shell model calculations, though modification of the single-particle energies, in particular, the $p\ensuremath{-}\mathrm{sd}$ shell gap, improves the agreement. The summed $B(E1)\ensuremath{\uparrow}$ value for these levels (in Weisskopf units) is consistent with that for other nuclei that have been discussed recently in the literature as potential Pygmy dipole resonance hosts.