Electron-Spin Magnetic Moments (g Factors) of the Oxides LiO, NaO, and the Superoxides LiO2, NaO2. An ab Initio Study

Abstract

The electron-spin magnetic moments of the superoxides LiO2 and NaO2, as parametrized by the g factors, are studied at the uncorrelated (ROHF) and correlated (MRCI) ab initio levels. The present method, which uses a perturbative approach complete to second order, is based on the Breit−Pauli Hamiltonian. In the standard C2v notation for the MO2 radicals, Δgyy > Δgzz ≫ |Δgxx|, where Δgaa = gaa − ge. The perpendicular component Δgxx, which is small and negative, is dictated by first-order terms (ground-state expectation values). The in-plane components Δgyy and Δgzz are large and positive. Δgyy is governed by the second-order magnetic coupling between X2A2 and 12B2 (electron excitation from the highest b2 MO into the a2(π*) SOMO), and Δgzz by the coupling with two 2A1 states (excitations from the two highest a1 MOs into π*). The calculated data reproduce the experimental trends reasonable well. For the ground state X2A2, the MRCI results for Δgxx, Δgyy, Δgzz (in ppm, with ppm = 10-6) are −373 (−350), 56 800 (...