Calculation of the thermodynamic functions from the Raman frequency shifts close to the epsilon - delta(loc) - delta transitions and Pippard relations in nitrogen

Abstract

Thermodynamic functions of the thermal expansion (alpha(p)), isothermal compressibility (kappa(T)) and the difference in the heat capacity (C-p - C-v) are calculated as a function of temperature (P = 18 GPa) close to the transitions of epsilon - delta(loc) and delta(loc)-delta in the solid nitrogen. This calculation is performed by using the observed Raman frequency shifts of vibrons (nu(1), nu(2) and nu(22)). Also, by using the observed V -P data, those thermodynamic functions are predicted at various pressures for the fluid-solid transition in nitrogen. For both calculations, observed data are used from the literature. From the temperature and pressure dependences of the thermodynamic functions studied, the Pippard relations are examined close to the epsilon - delta(loc) - delta transitions and also fluid-solid transition in nitrogen. We find that the thermodynamic functions can be predicted from the Raman frequency shifts and that the Pippard relations can be established for both the epsilon - delta(loc) - delta and fluid-solid transitions in nitrogen. This method of predicting the thermodynamic functions can also be applied to some other molecular solids.