Origins of structure in the e1 ionisation bands of magnesocene and osmocene. A photoelectron spectroscopic study of M(η−C5D5)2, MMg and Os Original Research Article

He I photoelectron spectra of the e1 bands of M(η−C5D5)2, MMg and Os, are reported and compared with those of the undeuterated analogues. In both cases, the observed fine structure is identical to that of the protonated analogue ruling out any CH vibrational excitation as its cause. The infrared spectra of both deuterated molecules are also reported. In the case of magnesocene, a vibrational sequence of 1452±200 cm−1 is observed in the e1g ionisation band, which corresponds most closely with that found for the E CC vibrations for the parent molecule. The E2g vibration is expected to be the Jahn-Teller active vibration in the molecular ion in a 2E1g excited state. This indicates that Jahn-Teller distortion of [Mg(η−C5H5)2]+ is dynamic rather than static. The e′1 ionisation band of Os(η−C5H5)2 and Os(η−C5H5)2 shows a second maximum 0.37±0.005 eV above the vertical ionisation energy, together with other fine structure. The fine structure in this case is assigned to spin-orbit coupling as a result of an Os p contribution to the e′1 wave function. The department from the anticipated 1-to-1 intensity is ascribed to the Ham effect.