  With angle resolved photoemission experiments and \emph{ab-initio} electronic
structure calculations, the pentacene monolayers on Ag(110) and Cu(110) are
compared and contrasted allowing the molecular orientation and an unambiguous
assignment of emissions to specific orbitals to be made. On Ag(110), the
orbitals remain essentially isolated-molecule like, while strong
substrate-enhanced dispersion and orbital modification are observed upon
adsorption on Cu(110). We show how the photoemission intensity of extended
systems can be simulated and that it behaves essentially like that of the
isolated molecule modulated by the band dispersion due to intermolecular
interactions.
