Infrared PhotodissociationSpectroscopy of MononuclearIron Carbonyl Anions.

The infrared photodissociation spectroscopy of mass-selectedmononucleariron carbonyl anions Fe(CO)n–(n= 2–8) were studied in the carbonyl stretchingfrequency region. The FeCO–anion does not fragmentwhen excited with infrared light. Only a single IR active band wasobserved for the Fe(CO)2–and Fe(CO)3–anions, consistent with theoretical predictionsthat these complexes have linear D∞hand planar D3hsymmetry, respectively. The Fe(CO)4–anion is the most intense peak in the mass spectra and was characterizedto have a completed coordination sphere with high stability. Anionclusters larger than n= 4 were determined to involvea Fe(CO)4–core anion that is progressivelysolvated by external CO molecules. Three CO stretching vibrationalfundamentals were observed for the Fe(CO)4–core anion, indicating that the Fe(CO)4–anion has a C3vstructure.All the carbonyl stretching frequencies of the Fe(CO)n–anion complexes are red-shiftedwith respect to those of the corresponding neutrals. [ABSTRACT FROM AUTHOR]