Diproton decay of nuclei on the proton drip line

The process of direct two-proton decay of nuclei with Z=22–28 on the proton drip line is considered. On the basis of new 0${\mathit{d}}_{3/2}$-0${\mathit{f}}_{\mathit{f}/2\mathrm{}}$ shell-model mass extrapolations, ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{42}{}_{}{}^{}\mathrm{Cr}$, ${}_{}{}^{45}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{49}{}_{}{}^{}\mathrm{Ni}$ are found to be bound to single-proton decay but unbound to two-proton decay. New estimates of the spectroscopic factors and lifetimes have been made. The decays of ${}_{}{}^{39}{}_{}{}^{}\mathrm{Ti}$, ${}_{}{}^{45}{}_{}{}^{}\mathrm{Fe}$, and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ni}$ are found to be promising for further experimental investigation.