Spin and Quadrupole Moment ofI125and the Magnetic Moment ofI131

The spin and quadrupole moment of ${\mathrm{I}}^{125}$ have been determined by observations on the microwave absorption spectrum of C${\mathrm{H}}_3$ ${\mathrm{I}}^{125}$. Five absorption lines have been observed which fit the quadrupole hyperfine pattern of the $J=2\mathrm{}\leftarrow 1$ rotational spectrum. The measurements indicate a spin of $\frac{5}{2}$ and a quadrupole coupling constant of -2179±1 Mc/sec. Using this and other known properties of the C${\mathrm{H}}_3$I molecule, the quadrupole moment of ${\mathrm{I}}^{125}$ is calculated to be -0.66×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$. This spin and quadrupole moment suggest a nuclear configuration for ${\mathrm{I}}^{125}$ similar to that of stable ${\mathrm{I}}^{127}$, i.e., predominantly $d_{\frac{5}{2}}$. The magnetic moment of ${\mathrm{I}}^{131}$ has been measured by observation of the Zeeman splitting of the $F=\frac{9}{2}\leftarrow \frac{9}{2}\mathrm{}(K=1\mathrm{})\mathrm{}$ hyperfine line of the $J=2\mathrm{}\leftarrow 1$ rotational spectrum of C${\mathrm{H}}_3$ ${\mathrm{I}}^{131}$. The magnetic moment is found to be 2.56±0.12 nuclear magnetons. The observations also confirm the previous results of Gordy et al. for the spin of ${\mathrm{I}}^{131}$ of $\frac{7}{2}$ and quadrupole coupling constant, $eqQ=-974\mathrm{}\pm 1$ Mc/sec. The magnetic moment measurement suggests a ground-state configuration similar to that of ${\mathrm{I}}^{129}$ which is predominantly $g_{\frac{7}{2}}$ in nature but with large admixture of other states. The significance of these results are discussed.