The experimental and theoretical literature on the molecular Zeeman effect is surveyed. The observation of the linear (H) and quadratic (H 2) Zeeman effect leads to a direct determination of the molecular g values, magnetic susceptibility anisotropies and molecular quadrupole moments. The recent results are discussed and the available molecular g values, magnetic susceptibility anisotropies, and molecular quadrupole moments are tabulated.

The molecular Zeeman effect in diamagnetic molecules and the determination of molecular magnetic moments (g values), magnetic susceptibilities, and molecular quadrupole moments

Molecular magnetizabilities have been calculated at the Hartree–Fock level for a series of diamagnetic molecules: H2O, NH3, CH4, PH3, H2S, CO2, CSO, CS2, and C3H4 Gauge invariance is imposed by the use of London atomic orbitals The results are compared to those obtained with the IGLO (individual gauge for localized orbitals) method and are found to converge faster to the basis set limit Magnetizabilities obtained from basis sets of different quality never differ by more than 4% for the London method, compared to 20% for IGLO The Hartree–Fock limit may be approached using London basis sets of moderate size, in contrast to calculations of molecular polarizabilities which require large basis sets to be reliable Comparison with experiment shows that the Hartree–Fock method overestimates experimental susceptibilities by 5%–10%

Hartree-Fock limit magnetizabilities from London orbitals

The structure of the CO2−, OCS−, and CS2− anions as well as the adiabatic electron affinities of the corresponding CO2, OCS, and CS2 neutral parents are computed using the infinite-order coupled-cluster method with all singles and doubles and non-iterative inclusion of triple excitations (CCSD(T)) and Hartree-Fock-Density-Functional-Theory (HFDFT) levels of theory. The potential energy curves of the CO2 – CO2− and CS2 – CS2− pairs are calculated as a function of the bending angle. All three anions are found to have bent equilibrium configurations. The adiabatic electron affinities of CO2 and OCS are calculated to be negative, whereas the CS2− anion is stable in the linear and relaxed geometries. The existence of CS2− at linear geometries can be related to experimental observations of an electric field-induced detachment of an extra electron from the anion in fields of only a few kilovolts per centimeter.

Electron affinities of CO2, OCS, and CS2

Magnetic Shielding and Susceptibility Anisotropies

Molecular beam electric resonance spectroscopy has been used to observe hyperfine, Stark, and Zeeman properties of chlorine monofluoride. The dipole moment from Zeeman data is 0.85(15), −FCl+, in agreement with the known magnitude. The sign obtained here is the opposite of earlier, less precise, Zeeman results but agrees with calculations and van der Waals molecule experiments. Hyperfine, Stark, and Zeeman properties for 35ClF and 37ClF are reported, including polarizability anisotropy, α∥−α⊥=1.32(8) A3, molecular quadrupole moment, ϑ∥=1.54(7) ×10−26 esu⋅cm2, and the chlorine quadrupole coupling constant derivative, deQq/dR=−90(20) MHz/A.

Molecular beam Zeeman effect and dipole moment sign of ClF

The molecular Zeeman effects of 16O12C32S and 16O12C34S have been observed under high resolution in magnetic fields up to 30 000 G. Conventional microwave spectroscopy is combined with a 6‐ft long magnet to yield accurate first‐ and second‐order magnetic field parameters. The magnetic susceptibility anisotropy of the OCS molecule is χ⊥–χ∥ = (9.27 ± 0.10) × 10−6erg/G2·mole. The molecular g values for the two isotopes obtained from the J = 0 → J =  transitions are g⊥(16O12C32S) = − 0.028711 ± 0.00004 and g⊥(16O12C34S) = − 0.028127 ± 0.00004. These data yield the sign of the molecular electric dipole moment which has −OCS+ polarity. Combining χ⊥–χ∥ and g⊥(16O12C32S) gives the molecular quadrupole moment of Q∥(16O12C32S) = − (0.88 ± 0.15) × 10−26esu·cm2.

Magnetic Susceptibility Anisotropy, Molecular Quadrupole Moment, and the Sign of the Electric Dipole Moment in OCS

The first‐ and second‐order molecular Zeeman effect has been observed in fluorobenzene to give the molecular g values of gaa = − (0.0670 ± 0.0008), gbb = − (0.0397 ± 0.0015), gcc = + (0.0266 ± 0.0017), and the magnetic susceptibility anisotropies of 2χaa − χbb − χcc = + (52.9 ± 0.8) × 10−6erg/G2·mole and 2χbb − χcc − χaa = + (63.6 ± 1.5) × 10−6erg/G2·mole. The a axis passes through the CF bond and the b axis is also in the molecular plane. Only the relative signs of the g values are obtained experimentally. However, by combining our magnetic susceptibility anisotropies with the average magnetic susceptibility we can show that the signs must be as assigned above. The diagonal elements in the total magnetic susceptibility tensor are χaa = − (40.6 ± 0.8) × 10−6, χbb = − (37.1 ± 0.8) × 10−6, and χcc = − (97.2 ± 2.0) × 10−6erg/G2·mole. The diamagnetic and paramagnetic susceptibilities are given as χaad = − (293.3 ± 1.7) × 10−6, χaap = (252.7 ± 0.7) ± 10−6, χbbd = − (509.7 ± 3.6) × 10−6, χbbp = (472.6 ± 2.6) × ...

P. D. Foster

Papers

Magnetic Susceptibility Anisotropy, Molecular Quadrupole Moment, and the Sign of the Electric Dipole Moment in OCS

Molecular g Values, Magnetic Susceptibility Anisotropies, and Molecular Quadrupole Moments in Fluorobenzene