Vibrational spectrum and structure of the Fe2CO molecule. An infrared matrix isolation and density functional theory study

The Fe2 + CO reaction has been reinvestigated using deposition of ground-state iron atoms and carbon monoxide in solid argon. The iron carbonyl products observed without activation energy are Fe2CO and higher carbonyl species Fe(CO)x. The Fe2CO molecule has been characterized through the observation of four fundamental transitions assigned to the three stretching (ν1, ν2, and ν4) and the highest frequency bending vibration (ν3). Isotopic data on ν1, ν2, ν3, ν4, ν1 + ν2, and 2ν1 have been measured in the near- and far-infrared regions. From the experimental data, a linear structure can be excluded and precise C−O, Fe−C, and Fe−Fe bond force constants can be determined. Geometrical and electronic configurations of the lowest energy states for each possible spin multiplicity of Fe2CO, Fe2CO-, and Fe2CO+ have been calculated using density functional theory with the generalized approximation for the exchange-correlation functional (DFT-GGA). The calculation results also predict an end-on, but highly bent, Fe−F...