Effects of vibrational intercentre interaction in a trigonal two-centre system with twofold electronic degeneracy at each centre

Abstract

The two-centre system formed by a pair of electronically degenerate metal ions and their surroundings, interacting via the common vibrational system and electron-electron coupling, is investigated. The centres are assumed to have a common symmetry axis of third order, each centre being in a non-Kramers doubly degenerate electronic state strongly coupled to doubly degenerate nearest-neighbour nuclear displacements of E type. The adiabatic potential-energy surface of the system is shown to have a one-dimensional ring continuum of minima (a trough), and the representative point rotates freely along the trough. This internal rotation corresponds to in-phase rotations of the nearest-neighbour nuclear distortions around the centres. The counterphase motion is reduced to hindered rotations or to localized vibrations at the bottom of the potential well, depending on the value of the intercentre coupling constant. The vibronic energy spectrum is obtained and the nature of the ground singlet vibronic state of the J...