Structural aspects of the magnetic and melting transitions in bilayer molecular oxygen on graphite

X-ray diffraction measurements are presented for bilayer oxygen adsorbed on the basal planes of exfoliated graphite. High resolution synchrotron data on the ζ to η and melting transitions suggests a model of two incommensurate-successive layers for the ζ and η phases. Lower resolution diffraction studies of the low temperature ε{lunate} phase confirm the Nielsen-McTague model for the structure. However, our results indicate that the ε{lunate}-ζ transition, which is presumably magnetic in origin, is first rather than second order. © 1984.