Macro-atom versus many-electron effects in ultrafast ionization of C60

Ionization mechanisms of C₆₀ molecules irradiated by a short intense 800-nm laser pulse are studied. Angle-resolved photoelectron spectra show above-threshold ionization (ATI) patterns with a low peak contrast and a remarkably smooth angular distribution. The results are interpreted by combining two theoretical models. A time-dependent Schrödinger equation (TDSE) calculation based on the B-spline method that explicitly takes into account the molecular potential mimics the single-active-electron response while a statistical model accounts for the many-electron effects. We show that the latter are responsible for the loss of contrast in the ATI peaks. The smooth angular distribution arises in the TDSE calculation as a result of the high angular momentum of the C₆₀ ground electronic state and therefore is a manifestation of the atomic behavior of the molecule.