From Simulation to Thermodynamics of Orientational Transitions in Molecular Layers: Nitrogen Contact Layer on Solids

Abstract

Orientational ordering is a well-known feature of polyatomic molecules in contact layers on solid surfaces. The majority of reported results refer to systems significantly depended on specific fluid–substrate interaction. An example is the nitrogen molecular layer commensurate with the graphite lattice at low temperatures. At the same time, it is instructive to analyze intrinsic thermodynamic properties of the molecular layer stabilized by a smooth substrate surface. In this study the nitrogen molecular layer is modeled by the Monte Carlo method with the emphasis placed on the orientational transition. The quadrupole–quadrupole interaction induces the herringbone orientational ordering which stretches the layer lattice along the glide line. The increase of temperature reduces the deformation, and its disappearance coincides with the transition from long- to short-range order. The magnitude of dispersion and electrostatic forces are always comparable even if the long-range ordering is absent, though the co...