Spectroscopic modifications of Pippard relations and their application to NH4Cl

Abstract

Abstract The Pippard relations have been reformulated in terms of the spectroscopic parameters and applied to the NH 4 Cl system in the vicinity of its λ-transition. We have effectively tested some of these relations in an earlier study where we have used, for the frequency shift, data for the ν 5 lattice mode of NH 4 Cl. Here, using our observed frequency shifts for the internal mode, ν 2 of NH + 4 , we have obtained a good fit to the Pippard relations for temperatures below T λ for the NH 4 Cl system. We have then been able to extract the frequency shift data for the ν 2 internal mode as a function of temperature, using the specific heat and also thermal expansion data from the literature. The method of analysis for obtaining the thermodynamic data from the spectroscopically measured quantities or vice versa is given here.