Orientational phases of a quadrupolar bilayer

Some structures and orientational phase transitions appropriate to close-packed molecular bilayers have been investigated by Monte Carlo calculations. The molecular bilayer is modeled by point quadrupoles arranged on two triangular nets whose lattice points have an ideal $\frac{c}{a}$ ratio. Both nearest-neighbor and second-neighbor electrostatic quadrupole-quadrupole interactions have been examined. We discuss the relevance of these calculations to experimental data for nitrogen physisorbed on the graphite basal plane.