DISSOCIATIVE PHOTOIONIZATION OF IRON PENTACARBONYL IN THE RANGE 38-120 EV

Dissociative photoionization processes of iron pentacarbonyl are inves tigated in the inner-valence region by use of the photoelectron-photoi on coincidence (PEPICO) and photoion-photoion coincidence (PIPICO) tec hnique combined with synchrotron radiation. Photon energy dependence o f the yield is examined in detail for all observed ions and ion pairs in the range 38-120 eV. Ions observed in the PEPICO measurements inclu de not only the fragment ions resulting from simple CO elimination but also those resulting from additional cleavage of the C-O covalent bon d(s) in the ligand. In the PIPICO measurements, several novel ion pair s that unambiguously indicate the cleavage of the covalent C-O bond in the ligated state are detected. From the analysis of these PEPICO and PIPICO efficiency curves, dissociation mechanisms leading to all ions and ion pairs are discussed, placing special emphasis on the cleavage of one or more covalent C-O bonds. It is concluded that the increased extent of the back-donation of d pi electrons of the central metal at om to the 2 pi antibonding orbital of CO plays an important role in t he C-O bond cleavage.