H. Martini et al., THEORETICAL INVESTIGATION OF FINE-STRUCTURE EFFECTS IN THE BENDING AND SYMMETRICAL STRETCHING VIBRONIC SPECTRUM OF FEH2 AND FED2, Molecular physics, 95(1), 1998, pp. 27-42
Two-dimensional potential energy surfaces were determined for the 25 s
patial and spin components of the low-lying electronic (5)Delta(g), (5
)Pi(g), and (5)Sigma(g)(+) states of iron dihydride along the bending
and symmetric stretching coordinates. Spin-free electronic energies an
d electric dipole moments were obtained by means of an averaged couple
d-pair functional employing a one-component relativistic Hamiltonian.
Diagonal and off-diagonal spin-orbit coupling matrix elements were eva
luated at the ab initio level for a variation of the symmetric stretch
ing coordinate while the dependence on the bending angle vias estimate
d from the variation of the angular momentum matrix elements. Vibronic
energy levels were calculated separately for each multiplet component
: for the treatment of Renner-Teller coupling in the large amplitude b
ending motion an effective Hamiltonian was used in which the symmetric
stretching motion is separated off and integrated over. We find that
the Renner-Teller coupling is negligible in the X(5)Delta(g) state and
that its vibronic energy level scheme is dominated by spin-orbit coup
ling effects. The spatial components of the excited (5)Pi(g) state, on
the other hand, exhibit a considerable energy separation upon bending
. Close to the (5)Pi(A2) component we locate the (5)Sigma(g)(+) electr
onic state which has large spin-orbit coupling matrix elements with bo
th (5)Pi(g) components.