The very neutron deficient $Z=N+1\mathrm{}$ nuclei ${}_{39}^{77}\mathrm{Y}$, ${}_{40}^{79}\mathrm{Zr}$, and ${}_{42}^{83}\mathrm{Mo}$ have been observed for the first time following the fragmentation of a ${}^{92}\mathrm{Mo}$ beam. In contrast, no evidence was found for the existence of ${}_{41}^{81}\mathrm{Nb}$ and ${}_{43}^{85}\mathrm{Tc}$. The observation of ${}_{39}^{77}\mathrm{Y}$ is of particular interest in light of the instability of the odd-proton, $Z=N+1\mathrm{}$ systems, ${}_{35}^{69}\mathrm{Br}$, ${}_{37}^{73}\mathrm{Rb}$, ${}_{41}^{81}\mathrm{Nb}$, and ${}_{43}^{85}\mathrm{Tc}$, and may be explained as a consequence of the shape polarizing effect of the highly deformed, prolate $Z=N=38\mathrm{}$ core. The experimental results are discussed within the framework of the shell-correction model, which together with proton-decay calculations allow an estimate of the proton separation energies of these highly exotic systems to be calculated.

• Received 23 April 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.295