Molecular terms, magnetic moments and optical transitions of molecular ions C60+/-

TL;DR

This paper presents detailed configuration interaction calculations of molecular ions C60+/-, analyzing their energy terms, magnetic moments, and optical transitions, and compares results with experimental data.

Contribution

It introduces a comprehensive theoretical framework for the electronic structure, magnetic, and optical properties of C60 ions, including new calculations of energy levels and transition lines.

Findings

Ground state of C60^{2-} is either 3 T1g or 1Ag.

Multiple low-lying triplet and quartet states are identified for different ions.

Optical transition lines are predicted and compared with experimental data.

Abstract

Starting from a multipole expansion of intra- molecular Coulomb interactions, we present configuration interaction calculations of the molecular energy terms of the hole configurations hu^m, m=2-5, of C60^{m+} cations, of the electron configurations t1u^n, n=2-4, of the C60^{n-} anions, and of the exciton configurations (hu^+ t1u^-), (hu^+ t1g^-) of the neutral C60 molecule. The ground state of C60^{2-} is either 3 T1g or 1Ag, depending on the energy separation between t1g and t1u levels. There are three close (~0.03 eV) low lying triplets 3T1g, 3Gg, 3T2g for C60^{2+}, and three quartets 4T1u, 4Gu, 4T2u for C60^{3+}, which can be subjected to the Jahn-Teller effect. The number of low lying nearly degenerate states in largest for m=3 holes. We have calculated the magnetic moments of the hole and electron configurations and found that they are independent of molecular orientation in respect to an external magnetic field. The coupling of spin and orbital momenta differs from the atomic case. We analyze the electronic dipolar transitions t1u^2 -> t1u t1g and t1u^3 -> t1u^2 t1g for C60^{2-} and C60^{3-}. Three optical absorption lines (3T1g -> 3Hu, 3T1u, 3Au) are found for the ground level of C60^{2-} and only one line (4Au -> 4T1g) for the ground state of C60^{3-}. We compare our results with the experimental data for C60^{n-} in solutions and with earlier theoretical studies.