Partial photoionization cross sections of C60 and C70: A gas versus adsorbed phase comparison

We have performed high resolution measurements of the photoelectrons emitted from the valence shell of C60 and C70, in the gas phase and adsorbed phase on a metal surface, in order to derive branching ratios and the partial photoionization cross sections of the two highest occupied molecular orbitals, HOMO and HOMO-1. The comparison between the gas phase and the adsorbed phase shows an interesting and unexpected difference that can be attributed to a small orbital shift in solid C70. Density Functional Theory calculations within the Local Density Approximation (LDA) show good agreement for both data sets and give a plausible explanation for the observed difference.