The electron-spin magnetic moments (g factors) of O3−, O3Li, and O3Na: An ab initio study

Abstract

The electron-spin magnetic moments of O3−, O3Li, and O3Na, as parametrized by the g factors, are studied at the uncorrelated restricted open Hartree–Fock (ROHF) and correlated multireference configuration interaction (MRCI) ab initio levels. The present method, which uses a perturbative approach complete to second order, is based on a Breit–Pauli Hamiltonian. The calculated Δg values, with Δg=g−ge, are very similar for all three species, confirming that the O3− moiety is retained in the ozonides O3M. In the standard C2v notation, Δgyy>Δgzz≫|Δgxx|. The perpendicular component Δgxx is small and negative, while the in-plane components Δgyy and Δgzz are large and positive. The MRCI results for Δgxx, Δgyy, Δgzz (in ppm) are: −475, 16 673, 10 121 for O3−; −679, 13 894, 9308 for O3Li; and −494, 12 298, 8690 for O3Na. The ROHF values of Δgyy and Δgzz are smaller than the MRCI data, due to a general overestimation of the excitation energies. The MRCI Δg values for isolated O3− reproduce the experimental results for O3− trapped in crystals or adsorbed on MgO surfaces (in ppm, −500–1200 for Δgxx, 12 400–16 400 for Δgyy, and 6900–10 000 for Δgzz). For O3Na, the experimental Δgxx, Δgyy, Δgzz data (−100, 14 200, 9800 ppm) are again satisfactorily described by our correlated results. No experimental g shifts are available for O3Li. In all systems studied here, the Δgxx component is dictated by first-order terms (ground state expectation values); Δgyy is governed by the second-order magnetic coupling between X 2B1 and 1 2A1 [electron excitation from the highest a1 molecular orbital (MO) into the b1(π*) singly occupied MO]; and Δgzz, by the coupling with two B22 states (excitations from the two highest b2 MOs into π*).