To understand the nature of the pseudo-Jahn−Teller (JT) effect,
an energy component analysis of the total
energy was carried out in the ground state of the titled ion radicals
by using the MCSCF method with 6-31G(d) basis set. Examination of the energy components comprising in
the total energy reveals that in the radicals
the stability of a less symmetrical nuclear configuration
(C
2
v
) is attributable
commonly to the energy lowering
of the internuclear repulsion term and the kinetic and interelectronic
repulsion terms due to σ electrons.
These observations are consistent with an expansion of the
molecular skeleton brought about by the pseudo-JT distortion. In the triafulvalene anion radical, it is further
found that the nuclear−electron attractive and
interelectronic repulsive terms due to π electrons also contribute to
the stability of the C
2
v
structure. In the
pentafulvalene cation and heptafulvalene anion radicals, on the other
hand, the interelectronic repulsive and
nuclear−electron attractive terms due to π electrons contribute to
the stability of the C
2
v
structure, respectively.
These differences are accounted for in terms of a charge
polarization attributed to the migration of π electrons.
Moreover, characteristic electronic properties inherent in the
radicals are discussed with much attention to
the charge and unpaired spin-density distributions in the distorted
C
2
v
structure.