Jahn–Teller interaction in ferricenium cation

Abstract

Analysis of optical measurements on ferricenium cation (symmetry group D5d) suggests the existence of an isolated 2E2g ground level, the nearest excited level being about 2000–4000 cm−1 away from it. Efforts to explain magnetic resonance and susceptibility measurements on the ion, however, require a 2A1g level to be the lowest and a low lying 2E2g level at about 200 cm−1 above ground. Thus there exists an apparent inconsistency between the two sets of results. A possible model is suggested here to overcome this inconsistency. It is proposed that the electronic spectrum of the ion as suggested by the optical measurements is basically correct. However, there exists a Jahn–Teller induced coupling of the ground electronic 2E2g level with vibrational modes of the complex. The ground spectrum is found to consist of two vibronic Kramers' doublets lying close together, one of which has a negligible orbital contribution to the magnetic moment similar to that expected from a Kramers' doublet of 2A1g origin.