The He(I) and He(II) high resolution photoelectron spectra of osmocene are reported. Vibrational fine structure is observed in all the valence metal-based ionizations and in the cyclopentadienyl π ionizations which derive from the e1g and e1u symmetry combinations. Analysis of the vibrational progressions found in the metal-based ionizations provides a measure of the force constants and vibrational frequencies for the metal-ring stretch in the positive ions. The vibrational analysis for the 2E 2(5/2) and 2E2(3/2) states of the osmocene cation [derived from the spin-orbit split ionization of the metal e2g (dx2-y2, dxy) set] indicates an 0.12 Å greater metal-ring bond length in the cation compared to the neutral molecule. The sharp 2A1(1/2) ionization [correlating with removal of an electron from the metal a1g (dz2) orbital] is observed to have a much shorter vibrational progression. The adiabatic ionization is the most intense (vertical) band of the series, indicating that there is no appreciable change in metal-ring bond distance upon ionization from the nonbonding a1g (dz2) orbital to produce the 2A1(1/2) cationic state. A large spin-orbit coupling is observed in the metal ionization region and a moderate amount in the cyclopentadienyl ring π ionization region. From evaluation of the spin-orbit coupling, the ionization band which correlates primarily with the e1g combination of the cyclopentadienyl π orbitals is shown to contain about 27% metal character. The spin-orbit coupling effects are negligible in the ionization which corresponds to the e1u combination of the ring orbitals, as expected from the lack of symmetry interaction with the metal d orbitals. The ionizations of this complex also provide experimental measures of relative metal-based and carbon-based ionization cross sections with He(I) and He(II) energy sources which are compared with theoretical calculations. All of the observations indicate that covalent bonding is more prevalent in osmocene than in ferrocene.
ASJC Scopus subject areas
- General Physics and Astronomy
- Physical and Theoretical Chemistry