α-γ Transition in Solid Nitrogen and Carbon Monoxide at High Pressure

Abstract

We have examined the stability of the experimentally observed $\gamma$ phase of solid nitrogen in order to test the validity of various forms of the intermolecular potential for N₂. It was found that a Lennard‐Jones repulsive potential between nonbonded atoms fails to explain the stability of the tetragonal $\gamma$ phase, whereas a parametric, shape‐dependent, hard‐core potential gives a satisfactory account of this high‐pressure phase of solid N₂. The behavior of solid nitrogen‐15 is discussed briefly. On the basis of the hard‐core potential one would predict that a $\gamma$ phase also exists for carbon monoxide, although at a very much higher pressure.