Is the FeC − 3 cluster linear? Theoretical study of the equilibrium structure and bonding of FeC − 3

Ab initio electron correlation methods and density functional theory are used to investigate the structure, bonding, and stability of FeC   − 3 . Theoretical calculations show that the ground state of the FeC   − 3anion strongly depends on the level of theory. The linear 4 Σ − state with an open configuration δ 2 σ 1 is predicted to be the ground state of FeC   − 3at the coupled‐cluster theory restricted to single, double, and noniterative triple excitations (CCSD[T])//CISD and multireference (MR) second‐order Moller–Plesset (MP2)//CAS self‐consistent field (SCF) levels. Next stable conformations are a C 2V ring structure II ( 4 B 2 ) and a C 2V structure III ( 4 A 2 ) in which Fe is bonded to one carbon atom of a triangular C 3 . However, CISD and CCSD//CISD calculations show that the C 2V ring structure II and the C 2V structure III are more slightly stable than is the linear structure I of FeC   − 3 . The harmonic vibrational frequencies and relevant vertical electron binding energies are reported. Possible detachment transitions in the photoelectron spectrum of FeC   − 3are discussed on the basis of current calculations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 275–279, 2003