Theoretical investigation of fine-structure effects in the bending and symmetric stretching vibronic spectrum of FeH2 and FeD2

Abstract

Two-dimensional potential energy surfaces were determined for the 25 spatial and spin components of the low-lying electronic 5δg, 5IIg, and 5σ+g states of iron dihydride along the bending and symmetric stretching coordinates. Spin-free electronic energies and electric dipole moments were obtained by means of an averaged coupled-pair functional employing a one-component relativistic Hamiltonian. Diagonal and oft-diagonal spin—orbit coupling matrix elements were evaluated at the ab initio level for a variation of the symmetric stretching coordinate while the dependence on the bending angle was estimated 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 bending 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 X5δg state and that its vibronic energy level scheme is dominated by spin-orbit coupling effects. The spatial components of the excited 5IIg state, on the other hand, exhibit a considerable energy separation upon bending. Close to the 5IIA2 component we locate the 5σ+g electronic state which has large spin-orbit coupling matrix elements with both 5IIg components. © 1998 Taylor & Francis Group, LLC.