Abstract
A study of FeCO+ and Fe+ using both the
second-order multi-configurational quasi-degenerate perturbation
theory (MC-QDPT2) method and the coupled cluster theory with single
and double replacements (augmented by perturbative triples) [CCSD(T)]
method are presented. An all-electron triple-f valence plus
polarization basis set was used in all calculations. The equilibrium
CCSD(T) geometry of FeCO+ is found to be linear
(4Σ−) with a Fe+ to CO distance
of 1.905 Å and a CO bond distance of 1.133 Å. The
dissociation energy of D0
of 4Σ− FeCO+ to
6D Fe+ and 1Σ+ CO is
predicted to be 28.8 kcal mol−1, which is within the
experimental range. Excited state properties including potential
energy surfaces and are predicted for the low lying sextet
De and quartet states of FeCO+. The first
excited state is predicted to be 4Δ with a of 17.6
kcal mol&munus;1. The De lowest sextet
state is predicted to be 6Δ with a of 12.3 kcal
mol−1. Several examples of
pathological D0 behavior at many levels of theory
have been discovered and are discussed.