Coexisting inequivalent orientations of C60 on Ag(001)

X-ray photoelectron diffraction has been used to determine the molecular orientation of C60 adsorbed as a monolayer on the Ag~001! surface. From an extended comparison to single scattering cluster calculations, we find the presence of two inequivalent prevailing molecular orientations of the C60 cage, as well as a considerable fraction of rotationally not-ordered molecules. In this system, scanning tunneling microscopy ~STM! investigations have shown the presence of two differently imaged molecules that the authors proposed to originate from different bonding states @E. Giudice et al., Surf. Sci. 405, L561 ~1998!#. Our analysis suggests a relation between imaging property and rotational order or not-order, while the two prevailing orientations are not distinguished by the existing STM data in this case.