Mass of astrophysically relevant ³¹Cl and the breakdown of the isobaric multiplet mass equation

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The mass of ³¹Cl has been measured with the JYFLTRAP double Penning trap mass spectrometer at the Ion-Guide Isotope Separator On-Line (IGISOL) facility. The determined mass-excess value, -7034.7(34) keV, is 15 times more precise than in the Atomic Mass Evaluation 2012. The quadratic form of the isobaric multiplet mass equation for the T=3/2 quartet at A=31 fails (χ²ₙ=11.6) and a non-zero cubic term, d=-3.5(11) keV, is obtained when the new mass value is adopted. ³¹Cl has been found to be less proton-bound with a proton separation energy of Sₚ=265(4) keV. Energies for the excited states in ³¹Cl and the photodisintegration rate on ³¹Cl have been determined with significantly improved precision using the new Sₚ value. The improved photodisintegration rate helps to constrain astrophysical conditions where ³⁰S can act as a waiting point in the rapid proton capture process in type I x-ray bursts.