FECN- AND FECNH- (N=3,4) - A PHOTOELECTRON SPECTROSCOPIC AND DENSITY-FUNCTIONAL STUDY

Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, MS K2-14, Richland, Washington 99352, and Department of Physics, Washington State University, Richland, Washington 99352 Photoelectron spectra of the title molecules are reported at 3.49 eV photon energy. Vibrational structures are resolved in the spectra of FeC3-- and FeC 3H-. The FeC4- spectrum is unusually broad, indicating a large equilibrium geometry change from the anion to the neutral states. The FeC4H spectrum exhibits a single strong feature. Theoretical studies using the density functional theory are carried out to determine the structures and bonding of these clusters. All the molecules in the anion ground states are found to be linear with the Fe atom bonded at one end. The Fe and C bonding involves strong Fe 4s and C sp interactions as well as considerable Fe 3 d and C π interactions. The n =3 species can be best characterized by cumulenic types of bonding with FeC3H also having an acetylenic isomer. The n= 4 species in the linear structures can be approximately described by diacetylenic types of bonding. Mulliken charge analyses indicate that the extra charge in all the anions enters mainly into the Fe 4s antibonding orbital, in agreement with the assignment that the threshold detachment takes place from the σ* orbital mainly between the Fe and C atoms. The vibrational structure resolved in the FeC3- spectrum yields a Fe-C stretching frequency of 700 (150) cm-1 for the first excited state of FeC3, in agreement with the Fe-C multiple bonding character. ©1995 American Institute of Physics.