  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 $3/2^+$
and we confirm the existence of an unresolved doublet close to 6.288 MeV
(E$_{r}^{\text{c.m.}} = -120$ keV) with J$^{\pi}$ = $1/2^+$ and a high-spin
state. Using these results, we demonstrate a significant factor of two decrease
in the reaction rate uncertainties at nova temperatures.
