Ab initio studies on the electronic structure of FeOH

The electronic structure of FeOH has been studied by using the all-electron multireference averaged coupled-pair functional (ACPF) method combined with the scalar-relativistic Douglas-Kroll-Hebeta (DKH) Hamiltonian. A linear geometry (ground state (6)Delta(7) RFe-O = 1.7501 Angstrom, RO-H = 0.9444 Angstrom) is found to be the most stable structure for FeOH. Relativistic effects must be taken into account in order to predict the correct ground state. Furthermore, inner-shell correlation effects are also important for the Fe-O bond of FeOH, i.e., the Fe-O distance is lengthened by at least 0.02 Angstrom when the iron 3s and 3p orbitals are frozen at the ACPF level. The calculated ionization energy IE (7.43 eV) and standard gas phase enthalpies of formation DeltaH(f)(0) (21.03 kcal/mol) are in good agreement with Gorokhov's measurement (IE: 7.6 +/- 0.3 eV, DeltaH(f)(0) 25.4 +/- 4.1 kcal/mol). The obtained Fe-OH dissociation energy D-0 (3.61 eV) agrees well with the recent experimental value 3.50 +/- 0.12 eV obtained by Schroder and Schwarz but exceeds the error bar of Murad's older measurement (3.33 +/- 0.17 eV) by 0.13 eV. (C) 2004 Elsevier B.V. All rights reserved.