Evidence for the existence of the astrophysically important 6.40-MeV state of S-31

Proton-unbound excited states of S-31 have been populated with the S-32(d, t)S-31 reaction at a beam energy of 24 MeV. Tritons corresponding to S-31 states with E-x(S-31) approximate to 6.3-7.1 MeV were momentum analyzed with a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph at six angles ranging from theta(lab) = 15 degrees to 58.5 degrees. We report a statistically significant detection of an astrophysically important state at E-x(S-31) = 6402 (2) keV, whose existence as a third state in this region has been under debate. Using updated A = 31 nuclear structure information, we present a new set of proposed S-31-P-31 mirror assignments for 31S, in which this state is tentatively assigned a spin of 7/2. This level, corresponding to a P-30 + p resonance at 271 keV, is likely to have a significant influence on the P-30(p, gamma)S-31 reaction rate in explosive hydrogen burning in classical novae.