THEORETICAL INTERPRETATION OF THE ELECTROABSORPTION SPECTRUM OF FULLERENE FILMS

A three-dimensional analogue of the Merrifield model of the coupling b etween the Frenkel and charge transfer (CT) excitations of a molecular crystal is used to calculate the electroabsorption (EA) spectrum of b uckminsterfullerene films. The approach is essentially nonempirical, w ith most of the input parameters estimated from theoretical calculatio ns or from independent experiments, but in doubtful cases a comparison of the calculated and experimental EA spectra guides the choice betwe en alternative sets of parameters. Semiquantitative agreement between the calculated and experimental EA spectra lends credence to the model , which can therefore be used to draw conclusions concerning the under lying physical mechanisms. The EA signal of the CT states is shown to be substantially affected by the off-diagonal CT interactions, and by interactions with the optically inactive Frenkel excitons, whose intra molecular parentage is tentatively assigned. The results confirm the v alidity of previous calculations of the electrostatic CT state energie s. (C) 1998 American Institute of Physics. [S0021-9606(98)71142-0]