Rotational Zeeman Effect in Methyl Iodide

We have observed the molecular $\mathrm{(J)}$ and nuclear $\mathrm{(I)}$ Zeeman effects in the strongly coupled $\mathrm{(F)}$ methy iodide molecule. The shielded $g$ value of the ¹²⁷I nucleus in methyl iodide is ${\text{(1\hspace{0.17em}−\hspace{0.17em}σ)g}}_I\text{\hspace{0.17em}=\hspace{0.17em}1.1220\hspace{0.17em}±\hspace{0.17em}0.0025}$ and the molecular $g$ values parallel and perpendicular to the symmetry axis are $g_{\Vert }\text{\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}0.271\hspace{0.17em}±\hspace{0.17em}0.015}$ and $g_{\perp }\text{\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}0.010\hspace{0.17em}±\hspace{0.17em}0.002}$ . An upper limit of ${\mathrm{|\hspace{0.17em}\chi }}_{\Vert }{\mathrm{\hspace{0.17em}-\hspace{0.17em}\chi }}_{\perp }{\text{\hspace{0.17em}|\hspace{0.17em}=\hspace{0.17em}20\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−6}}\mathrm{erg}/{\mathrm{G}}^2·\mathrm{mole}$ has been obtained for the magnetic‐susceptibility anisotropy. Evidence is also presented on a possible observation of the magnetic‐shielding anisotropy.