Fine and Hyperfine Structure of the3P2Term in Lithium

Abstract

The fine and hyperfine structures of the $3{}_{}{}^2{}_{}{}^{}p$ term in ${\mathrm{Li}}^7$ have been studied by the technique of level-crossing spectroscopy. A preliminary value for the fine-structure separation is $\Delta \nu =2882.9\mathrm{}\pm 1.2$ Mc/sec. It is expected that the present technique can be extended to obtain a result that is reliable to a few parts per million. It is noteworthy that the fine-structure intervals in lithium are 8% and 12% smaller for the $2p$ and $3p$ levels, respectively, than the corresponding intervals in hydrogen. A theory is developed for interpreting the separation between hyperfine level crossings. Its application depends on a detailed knowledge of the core-polarization effects of the $3p$ electron. Evidence is presented indicating that the core-polarization effects in the $\mathrm{np}$ states $n=2,3\mathrm{}$ scale as ${〈\frac{1}{r^3}〉}_{\mathrm{np}}$ for the valence electron. Assuming this to be true, we estimate that $a_e\mathrm{}\left(3p\right)=-3.05\mathrm{}\left(12\right)\mathrm{}$ Mc/sec for ${\mathrm{Li}}^7$. The limited precision achieved so far in this work has prevented observation of the ${\mathrm{Li}}^7$ quadrupole interaction.