Level Structure ofLi6

A theoretical level structure for ${\mathrm{Li}}^6$ is calculated for the Hu-Massey Gaussian-shape tensor potential and for the Pease-Feshbach Yukawa interaction. The central force splittings are assumed equal to the first-order Majorana separation. The additional splittings produced by the tensor force of the $S$ and of the $D$ states of ${\mathrm{Li}}^6$ are computed by using a variational method which includes the effect of configuration interaction. An $S$-state splitting of approximately 2 Mev is found, when the Pease-Feshbach potential is used, with 9% admixture of excited states introduced into the zero-order wave functions. It is shown that the tensor force has little effect on the separation of the ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ states. For the Hu-Massey potential, the triplet $D$ states are split in essentially the same way as would result in first order from a vector-type spin-orbit force. In the case of the Pease-Feshbach potential, the effective first-order potential also includes a tensor term, smaller than and opposite sign to the original tensor force. With both potentials, a total multiplet splitting of about 1 Mev is obtained, with the ${}_{}{}^3{}_{}{}^{}D_3^{}{}_{}{}^{}$ state lowest.