Spin-parities of sub-threshold resonances in the ${}^{18}$F(p, $\alpha$)${}^{15}$O reaction

The ${}^{18}$F(p, $\alpha$)${}^{15}$O reaction is key to determining the ${}^{18}$F abundance in classical novae. However, the cross section for this reaction has large uncertainties at low energies largely caused by interference effects. Here, we resolve a longstanding issue with unknown spin-parities of sub-threshold states in ${}^{19}$Ne that reduces these uncertainties. The ${}^{20}$Ne(${}^3$He, ${}^4$He)${}^{19}$Ne neutron pick-up reaction was used to populate ${}^{19}$Ne excited states, focusing on the energy region of astrophysical interest ($\approx$ 6 - 7 MeV). The experiment was performed at the Triangle Universities Nuclear Laboratory using the high resolution Enge split-pole magnetic spectrograph. Spins and parities were found for states in the astrophysical energy range. In particular, the state at 6.133 MeV (E${}_r^{\text{c.m.}}=-278$ keV) was found to have spin and parity of $3\mathrm{/}{2}^{+}$ and we confirm the existence of an unresolved doublet close to 6.288 MeV (E${}_r^{\text{c.m.}}=-120$ keV) with J${}^{\pi }$ = $1\mathrm{/}{2}^{+}$ and a high-spin state. Using these results, we demonstrate a significant factor of two decrease in the reaction rate uncertainties at nova temperatures.