Analysis of a relatively well-resolved molecular beam electric resonance spectrum of ${\mathrm{Li}}^6$F $v=0\mathrm{}$, $J=1\mathrm{}$; $M_J=0\mathrm{}\to \left|M_J\right|=1\mathrm{}$ yields $eqQ=7.3\mathrm{}\pm 0.4$ kc/sec. Comparison of the coupling constants in ${\mathrm{Li}}^6$F and ${\mathrm{Li}}^7$F gives the ratio quadrupole moments of the two stable lithium isotopes to be $\frac{Q\left({\mathrm{Li}}^6\right)}{Q\left({\mathrm{Li}}^7\right)}=+0.0176\mathrm{}\pm 0.001$. This value is in good agreement with the earlier determination of sign by Kusch and magnitude by Cranna. Combining the measured quadrupole coupling constant in LiH with the electric field gradient calculated by Nesbet and Kahalas yields the nuclear quadrupole moments $Q\left({\mathrm{Li}}^6\right)=-8.0\mathrm{}\times {10}^{-28\mathrm{}}$ ${\mathrm{cm}}^2$ and $Q\left({\mathrm{Li}}^7\right)=-4.5\mathrm{}\times {10}^{-26\mathrm{}}$ ${\mathrm{cm}}^2$. The errors in both quadrupole moments are estimated to be ±10%.

• Received 9 September 1963

DOI:https://doi.org/10.1103/PhysRev.133.B270