Oscillations in the valence-band photoemission spectrum of the heterofullereneC59N:A photoelectron interference phenomenon

The intensities of the two strongest low-binding energy features in the valence-band photoemission spectra of ${\mathrm{C}}_{59}\mathrm{N}$ have been observed to oscillate as the photon energy of the exciting radiation is varied. The maxima in the intensity ratio of the two peaks occur at the same photon energies as the maxima in the intensity ratios of the highest occupied molecular orbitals to next highest occupied molecular orbitals (NHOMO) peaks of ${\mathrm{C}}_{60}.$ The amplitude of modulation of the ratio is remarkably similar in both cases. Since the nature of the filled and empty states involved in the photoemission process are different for ${\mathrm{C}}_{59}\mathrm{N}$ compared to ${\mathrm{C}}_{60},$ the current observation therefore supports the proposal that the final state is of negligible importance in the mechanism leading to the oscillations. The intensity variation instead arises from a photoelectron interference effect as a consequence of the spherical environment of the electron emitters within the molecule.