A Monte Carlo simulation study of Nitrogen on LiF(0 0 1)

The adsorption of N2 gas on the LiF(0 0 1) surface is studied by canonical Monte Carlo (CMC) computer simulation. These results show that N2 forms an ordered structure where the molecules are arranged in a unit cell of p(22×2)R45° symmetry at temperatures below 23 K with 50% coverage. The nitrogen molecules are tilted by 53° from the surface normal and have the same azimuthal orientation along diagonals, with diagonals alternating their orientation. Beyond 23 K, the molecules become azimuthally disordered but with residual short-range order. No change in the position of the peak of the polar (tilt) angle distribution was observed above the transition temperature. This transition is purely of the order-disorder type.