The technique of level crossing spectroscopy has been used to study the hyperfine structure of the $3{}_{}{}^2{}_{}{}^{}P$ and $4{}_{}{}^2{}_{}{}^{}P$ states of ${\mathrm{Li}}^7$ and the $3{}_{}{}^2{}_{}{}^{}P$ state of ${\mathrm{Li}}^6$. Both low-field (<2 G) and high-field (≈915 G) level crossings were observed for the $3{}_{}{}^2{}_{}{}^{}P$ state of ${\mathrm{Li}}^7$. With the assumption that the ordinary magnetic-dipole coupling constants are related by $a_{\frac{d1\mathrm{}}{2}}=5\mathrm{}{a}_{\frac{d3\mathrm{}}{2}}$, values have been obtained for $a_{\frac{d3\mathrm{}}{2}}$ and the core-polarization constant $a_c$. In the $4{}_{}{}^2{}_{}{}^{}P$ state of ${\mathrm{Li}}^7$ and the $3{}_{}{}^2{}_{}{}^{}P$ state of ${\mathrm{Li}}^6$ we have inferred from our measurements individual values for $a_{\frac{d3\mathrm{}}{2}}$ and $a_c$ which are consistent with the assumptions that both constants scale as the ratio of nuclear $g$ factors among different isotopes and that they scale as $\frac{1}{n^3}$ among all the $n{}_{}{}^2{}_{}{}^{}P$ states. The lifetime of the $3{}_{}{}^2{}_{}{}^{}P$ state has also been obtained from the high-field level crossing data. The results for the hyperfine constants in MHz are the following: $3{}_{}{}^2{}_{}{}^{}P$ ${\mathrm{Li}}^7$: $a_{\frac{d3\mathrm{}}{2}}=2.11\mathrm{}\left(3\right)\mathrm{}$, $a_c=-3.08\mathrm{}\left(3\right)\mathrm{}$, $4{}_{}{}^2{}_{}{}^{}P$ ${\mathrm{Li}}^7$: $a_{\frac{d3\mathrm{}}{2}}=0.89\mathrm{}\left(2\right)\mathrm{}$, $a_c=-1.30\mathrm{}\left(2\right)\mathrm{}$, $3{}_{}{}^2{}_{}{}^{}P$ ${\mathrm{Li}}^6$: $a_{\frac{d3\mathrm{}}{2}}=0.80\mathrm{}\left(2\right)\mathrm{}$, $a_c=-1.20\mathrm{}\left(2\right)\mathrm{}$. The lifetime of the $3{}_{}{}^2{}_{}{}^{}P$ state is $\tau \left(3\mathrm{}{}_{}{}^2{}_{}{}^{}P{\mathrm{Li}}^7\right)=182\mathrm{}\left(6\right)\mathrm{}$ nsec.

• Received 16 June 1969

DOI:https://doi.org/10.1103/PhysRev.187.76