Spectroscopic study of oxygen and fluorine isotopes with the (α,3He) and (α,t) reactions onO16,17,18

The (α${,}^3$He) and (α,t) reactions on ${}_{}{}^{16,17,18}{}_{}{}^{}\mathrm{O}$ were studied at ${\mathit{E}}_{\mathrm{\alpha }}$=65 MeV. Measured cross sections for the states up to 15 MeV in the residual nuclei were analyzed with the distorted wave Born approximation theory. Many spin-parity and isospin assignments were proposed based on the strengths, angular distributions, and excitation energies. Nearly equal spectroscopic factors were obtained for bound and unbound analog pairs except for the $2_1^{+}$, T=1 states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{18}{}_{}{}^{}\mathrm{F}$. Almost full strengths were observed for the 0${\mathit{d}}_{5/2}$, 1${\mathit{s}}_{1/2}$, and 0${\mathit{d}}_{3/2}$ transfers. The obtained spectroscopic factors for the 0${\mathit{d}}_{5/2}$ and 1${\mathit{s}}_{1/2}$ transfers were in good agreement with shell-model calculations, while the agreement was unsatisfactory for the 0${\mathit{d}}_{3/2}$ transfer in many respects. The ${\mathit{d}}_{3/2}$ strengths in ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{17}{}_{}{}^{}\mathrm{F}$ were more fragmented than the shell-model prediction, while only half of the expected 0${\mathit{d}}_{3/2}$ strength was found in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{O}$. The strength to the first excited 3/$2^{+}$, T=1/2 state in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ was twice that predicted. Spectroscopic factors for many 0${\mathit{f}}_{7/2}$ transitions were also deduced. The 14.1 and 14.3 MeV states in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, in particular, proposed to be the stretched $6^{\mathrm{-}}$ states in a recent (e,e’) experiment, were found to be excited by pure l=3 transfer with spectroscopic factors 0.16 and 0.05, respectively.