Electron-spin magnetic moments of the2?+ ions Li2+, Li2?, and Be2+: An ab initio ROHF study

For the 2Σ+ ground states of the ions Li2+, Li2−, and Be2+, the dependence of the magnetic moment (parametrized by g-shifts) on the bond length R was studied at the ROHF level. The Δ g-values were calculated via a perturbative approach (complete to second order in Breit-Pauli interactions) using quadruple-zeta AO basis sets augmented by semidiffuse and polarization functions. All Δ g-values in these systems are negative. The parallel component Δ g∥ generally changes little with R, remaining close to the g-shift of the corresponding 2S atomic dissociation product. For Li2+ and Be2+, the perpendicular component Δ g ⟂ is more sensitive to geometry than is Δ g∥, mainly because of the second-order magnetic coupling with excited 2Π states. For Li2−, Δ g ⟂ and Δ g∥ are similar due to the large size of the 2σu, SOMO, resulting in g-values close to that of a free electron.