The level spectra of neutron-rich Sb isotopes have been investigated within a shell-model space containing cross-shell excitations and the intruder orbit
. High-spin levels (27/2
) and (29/2
) in
Sb are taken over by the monopole effect induced by orbit
. The ground state and excited levels in
Sb are well improved by considering the monopole correction between neutron orbits
and
. The energy shrinking of the first excited state 5/2
in
Sb isotopes is explained by the
shift due to the attractive
monopole interaction when increasingly more neutrons occupy orbit
. The ground state of
Sb is predicted as 5/2
owing to the shrinking of the 5/2
states in Sb isotopes that causes ground state inversion when N = 88. Further monopole effects extend the applicable range of the present Hamiltonian to nuclei with more neutrons above the N = 82 shell. This Hamiltonian will be public, and researchers are encouraged to contact the authors.