  Low-lying continuum states of exotic oxygen isotopes are studied, by
introducing the Continuum-Coupled Shell Model (CCSM) characterized by an
infinite wall placed very far and by an interaction for continuum coupling
constructed in a close relation to realistic shell-model interaction. Neutron
emission spectra from exotic oxygen isotopes are calculated by the
doorway-state approach in heavy-ion multi-nucleon transfer reactions. The
results agree with experiment remarkably well, as an evidence that the
continuum effects are stronger than $\sim$1 MeV, consistently with the shell
evolution in exotic nuclei. The results by this CCSM doorway-state approach are
compared with calculations on neutron-scattering resonance peaks made within
the CCSM phase-shift approach and also with those obtained in the Gamow shell
model, by taking the same interaction. Remarkable similarities in peak energies
and certain differences in widths are then obtained.
