A density functional study of FeCO, FeCO−, and FeCO+

The binding energies, structural parameters, and vibrational frequencies of FeCO, FeCO−, and FeCO+ were studied with a linear combination of Gaussian-type orbitals-density functional (LCGTO-DF) method. The ground state of FeCO is found to be 3Σ− and the calculated dissociation energy, with respect to ground state Fe(5D,3d64s2) and CO (1Σ+), is 30 kcal/mol; after correcting for the atomic states separation of the iron atom this value becomes 17 kcal/mol, which is relatively close to the most recent experimental values 8.1±3.5–10.5±3.7 kcal/mol. Quartet ground states were found for both FeCO+ and FeCO− and the calculated dissociation energies (with respect to ground state Fe+, Fe−, and CO) are 50 and 31 kcal/mol, respectively. There is agreement between theory and experiment in that D(FeCO+)≳D(FeCO−)≳D(FeCO). The ωe’s we calculate for FeCO are, in cm−1, 658 (Fe–C stretch), 1982 (C–O stretch), and 368 (bend). These values are reasonably close to their experimental counterparts, 530±10, 1950±10, and 330±50. For FeCO− we have found 566 and 272 cm−1 for the Fe–C stretch and bend modes while the experimental values are 465±10 and 230±40 cm−1. A frequency of 1831 cm−1 is predicted for the C–O stretch of FeCO−. The σ-donation (CO→Fe) and π-back-donation (Fe→CO) charge transfer mechanism is operative in these species.