Photoionization of Ferrocene by Using Synchrotron Radiation

The vacuum ultraviolet photoionization of ferrocene has been studied by using synchrotron radiation and a time-of-flight（TOF）mass spectrometer. The photoionization TOF mass spectrum and photoionization efficiency （PIE）curves of some ions were measured. VUV absorption by ferrocene results in Fe（C5H5）2+，FeC5H5+，Fe+，FeC3H3+，FeC3H+，C10H9+，C10H8+ and C5H6+. The ionization potential（IP）of ferrocene is determined to be （6.78±0.05）eV. The appearance potential（AP）of the fragment FeC5H5+ was measured to be（13.40±0.10）eV. In addition，theoretical calculations with the density functional method B3LYP and the basis set 6-31G（d）have been carried out. The calculation result shows that the ionization potential of ferrocene is 6.16 eV，which is smaller than that from the experiment because the ionization potential from calculation is adiabatic value and the experimental result is vertical value. Due to the limited available computational cost，the case of the electron spin S=1/2 for Fe is only considered，which may lead to some low precision in calculation. So the calculation result is just as references. The appearance potential of FeC5H5+ is 12.17 eV，which is also smaller than the experimental value. According to the experimental and calculation results，the bond energies of D0（FeC5H5+-C5H5），D0（Fe+-C5H5），D0（C5H5-Fe+-C5H5）have been evaluated and the possible channels of dissociation photoionization have been analyzed. Sequential elimination of C5H5 ligands is a major dissociation channel，but concerted elimination of two C5H5 ligands also takes place.