Low-frequency and long-wavelength anomalies of the integral quantum Hall effect

We present model calculations of the orientational potential of reference molecules sited at both of the two crystallographic positions of the cubic δ phase of nitrogen, displaying either spherical (2a-sites) or disclike (6c-sites) disorder. The single particle orientational potential obtained exhibits characteristic differences for the two crystallographic sites. The local energy barriers for the reorientation of the molecules were used to construct the p - T phase boundary line, first, between the δ and ? phase and, second between the phase with an almost free molecular reorientation and the one with orientational localization within the gδ phase observed in recent Raman investigations of solid nitrogen.