Low States ofLi7in Intermediate Coupling

The intermediate-coupling transition of the five lowest levels of ${\mathrm{Li}}^7$-${\mathrm{Be}}^7$ is discussed. Some analytical emphasis is placed on the approach from the ($\mathrm{jj}$) coupling extreme with ordinary (nonexchange) interactions, in which case there is a first-order degeneracy which might have helped explain the scarcity of low levels, but second-order perturbations are shown to be too large. The only possibility of obtaining just two isolated low levels with either ordinary or Majorana interactions lies near the ($\mathrm{LS}$) coupling extreme, with angular momentum $I=\frac{1}{2}$ for the excited state.