The study of the vibronic problem and ESR behaviour of in cubic symmetry

Abstract

The and levels of in cubic symmetry are both susceptible to Jahn-Teller interaction due to the twofold degenerate and threefold degenerate vibrations. In addition to this the two levels are admixed under threefold degenerate odd vibrations of type. An analysis of this problem has shown the possibility of coexistence of two types of site, one having a trigonal type of ground state and the other of orthorhombic type. The ground vibronic levels at the two sites are capable of providing identical broad ESR signals. The sharp line in the spectra, known as a narrow spike, originates from the excited vibronic level, available only at sites with a trigonal type of ground state. The ground states of the similar vibronic problem of in icosahedral symmetry are of trigonal type resulting in a vibronic ground and an excited level (symmetry group ). Hence an isolated , i.e. without alkali ion ligands, is also capable of providing both broad and sharp ESR signals.