Large-basis shell model studies of light nuclei with a multivaluedG-matrix effective interaction

Large-basis shell model studies of low-lying excitations in light nuclei from ⁴He to ⁷Li have been performed with a multivalued G-matrix effective interaction, as recently suggested by Haxton et al. Calculations were performed relative to the vacuum (``no core'') using very large, separable model spaces containing all excitations with unperturbed energies up to 8{}{Ω}. Using G matrices derived from a new Nijmegen potential, we achieve a very satisfactory description of these excitations.