Low States ofLi7in Intermediate Coupling

Abstract

The intermediate-coupling transition of the five lowest levels of Li 7 -Be 7 is discussed. Some analytical emphasis is placed on tie approach from the (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 (LS) coupling extreme, with angular momentum /= 1/2 for the excited state.

Spin-Orbit Coupling inLi7andBe7

“…A strong admixture would lower the symmetry of the ground doublet and by altering the factor | might increase the magnetic term enough to bring about agreement with the Li 7 -Be 7 difference. Mixtures, in general, are expected to remove the isolation of the ground doublet by complicating the spectrum, 25 but such a special admixture might not-considered as a second-order perturbation it would depress the ground doublet, perhaps more than the next 2 F because there is only one 2 F in the configuration.…”

“…We then have 23 ((l/rXdV/dr^^^^Ea^ (er/Vo) 2 0.9 mc 2 . (25) Thus, with Ed'^lSao-1 mc 2 , JS/= 1.45(7<f* mc 2 , and J2o"=85.5 mc 2 , we have from (4) the expansion contribution to the excitation difference…”