ANALYSIS OF MOSSBAUER DATA OF BIFERROCENIUM SALTS USING A COOPERATIVE2-ORBITAL VIBRONIC PIEPHO-KRAUSS-SCHATZ MODEL

We analyze the Mossbauer quadrupole data of several biferrocenium salt s, using a recent two-orbital extension of a previous cooperative vibr onic Piepho-Krausz-Schatz (PKS) model. A discontinuous (continuous) lo calized-delocalized transition is described in terms of an order-disor der transition of first (second) order. The first-order results from a crossover of vibronic states based on the two orbitals. The thermal v ariations of the specific heat are calculated and compared to the avai lable experimental data.