ENERGY COMPONENT ANALYSIS OF THE PSEUDO-JAHN-TELLER EFFECT IN THE GROUND-STATE OF THE TRIAFULVALENE ANION, PENTAFULVALENE CATION, AND HEPTAFULVALENE ANION-RADICALS

To understand the nature of the pseudo-Jahn-Teller (JT) effect, an ene rgy component analysis of the total energy was carried out in the grou nd state of the titled ion radicals by using the MCSCF method with 6-3 1G(d) basis set. Examination of the energy components comprising in th e total energy reveals that in the radicals the stability of a less sy mmetrical nuclear configuration (C-2v) is attributable commonly to the energy lowering of the internuclear repulsion term and the kinetic an d interelectronic repulsion terms due to sigma electrons. These observ ations are consistent with an expansion of the molecular skeleton brou ght about by the pseudo-JT distortion. In the triafulvalene anion radi cal, it is further found that the nuclear-electron attractive and inte relectronic repulsive terms due to pi electrons also contribute to the stability of the C-2v, structure. In the pentafulvalene cation and he ptafulvalene anion radicals, on the other hand, the interelectronic re pulsive and nuclear-electron attractive terms due to pi electrons cont ribute to the stability of the C-2v structure, respectively. These dif ferences are accounted for in terms of a charge polarization attribute d to the migration of pi electrons. Moreover, characteristic electroni c properties inherent in the radicals are discussed with much attentio n to the charge and unpaired spin-density distributions in the distort ed C-2v structure.