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Note on the Li 7 Quadrupole Moment

1950; American Institute of Physics; Volume: 80; Issue: 1 Linguagem: Inglês

10.1103/physrev.80.43

1536-6065

R. D. Present,

Advanced Chemical Physics Studies

Recent measurements unexpectedly determine the sign of the quadrupole moment as positive, although the magnitude is uncertain. On the quasi-atomic model the ground state is $1{s}^{4}2{p}^{3}^{2}P_{\frac{3}{2}}$ and of symmetry [3] in Wigner's "first approximation." The corresponding quadrupole moment is -6 in units of $\frac{{〈{r}^{2}〉}_{2p}}{25}$. The explanation of the discrepancy is sought in configuration interaction. A variational calculation of the moment has been made taking into account the $P$ states of symmetry [3] from the low configurations $1{s}^{4}2{p}^{2}3p$ and $1{s}^{4}2{p}^{2}4f$. The maximum value of the moment is +2.32 in the above units; this value is increased by including other configurations. The admixture of [3] $P$ states from excited configurations has no effect on the magnetic moment nor on the matrix element for ${\mathrm{Be}}^{7}$ $K$-capture into the ground state of ${\mathrm{Li}}^{7}$; this is satisfactory since the quasi-atomic model agrees reasonably well with experiment in these instances. When the [3] $D$ states from the above configurations are included in the variational calculation, the maximum is raised to 8.03. The configuration interaction need not be large in this case to produce a positive moment; however the inclusion of the [3] $D$ states does impair the agreement with the magnetic moment and the $K$-capture data. Considering the wide margin of uncertainty in the estimated experimental quadrupole moment, we find that all the data are adequately explained without assuming large spin-orbit interaction or large departures from partition symmetry.