Pippard relation modified for the rotatory lattice mode in ammonia solid II

In this study we obtain a linear variation of the specific heat Cp with the Raman frequency shifts 1/v (partial derivative v/partial derivative T)p for the rotatory lattice (librational) mode in the ammonia solid II near the melting point. From this linearity, we deduce values of the slope dP(m)/dT for the pressures of 3.65, 5.02 and 6.57 kbars in the ammonia solid II. Our calculated value of dP(m)/dT for the pressure of 3.65 kbar, is in good agreement with the experimentally measured value in the P-T phase diagram of this crystalline system. This indicates that the first Pippard relation modified for the rotatory lattice mode in the ammonia solid II, is satisfactory near the melting point.