Intruder-driven mirror energy differences between 29Cl and 29Mg studied with antisymmetrized molecular dynamics

To clarify the mirror energy differences (MEDs) of the proton-unbound nucleus ²⁹Cl and their microscopic origins, we investigate the low-lying states of the ²⁹Cl-²⁹Mg mirror pair using antisymmetrized molecular dynamics. The calculation reasonably reproduces the normal and intruder states of ²⁹Mg, while suggesting alternative spin-parity assignments for ²⁹Cl. The 1/2⁺ and 3/2⁺ states are predicted to form a nearly degenerate ground-state doublet with a small MED because of their similar intrinsic structures. In contrast, the 3/2⁻ and 7/2⁻ intruder states exhibit large negative MEDs and are assigned to the observed resonances at approximately 500~keV and 1.1~MeV, respectively. Their large MEDs originate from the reduced Coulomb energies associated with the stronger deformation and spatially extended proton distributions in the intruder configurations.