Low-lying E1 strength in 20O -: art. no. 064309

Intermediate energy Coulomb excitation at 100 MeV/nucleon was used to probe the low-lying level structure of both O-18 and O-20 in the region between 1 and 8 MeV. Discrete 1(-) states with energies of 5.35(10) and 6.85(5) MeV were observed in O-20. The strong direct excitation and subsequent gamma-ray decay of these states, along with B(Elambda) predictions for O-18,O-20 levels in this energy region, established their dipole character. The extracted B(E1)up arrow values of 0.062(16)e(2) fm(2) and 0.035(9)e(2) 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-sd shell gap, improves the agreement. The summed B(E1)up arrow 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.