Knowledge Bank

The molecular Zeeman effect has been studied in several linear molecules which have strong nuclear quadrupole coupling of a nucleus to the rotational motion. A least squares computer fit of the magnetic field induced frequency shifts of the microwave lines yields the following Zeeman parameters: the shielded nuclear g value of the coupled nucleus, $g1(l-\sigma )$; the molecular g value, $g1$, and the magnetic susceptibility anisotropies, $\chi +-\chi$. The values of the parameters for the molecules ClF, BrF, ClCN, BrCN, and ICN are listed in a table below. For ICN, we were also able to measure the anisotropy in the magnetic shielding, $\Delta \sigma$. From the Zeeman parameters we calculate molecular quadrupole moments, anisotropies in the charge distribution, and contributions to $g1$ caused by the admixture of excited electronic states. Dipole moment signs are determined for ClF and ClCN. All the elements of the susceptibility tensor are calculated for ClCN, where the bulk susceptibility is known. The observed trends in the molecular constants are discussed. “figure”