  The impact of van der Waals interaction on the electronic structure between a
pentacene monolayer and a graphite surface was investigated. Upon cooling the
monolayer, newly formed dispersive bands, showing the constant final state
nature overlapping with the non-dispersive, discrete molecular orbital state,
is observed by low-energy angle-resolved photoelectron spectroscopy. The
dispersive band consists of positive and negative intensities depending on the
final state energy, indicating Fano resonance involving a discrete molecular
state that couples a continuum state upon photoionization. A wave-function
overlap is demonstrated according to their larger spread in unoccupied states
even at the weakly bounded interface by Fano spectral analysis.
