Raman bandwidths calculated for the librational (α-phase) and internal (Ɛ, δloc and δ phases) modes in solid N2 using pseudospin-phonon coupling (PS) and energy-fluctuation (EF) models

Abstract

This study gives the calculation of the Raman bandwidths using the models of the pseudospin-phonon coupling (PS) and energy fluctuation (EF) where the Raman frequency calculated from the molecular field theory, is considered as the order parameter close to the phase transitions in nitrogen. In particular, we study the temperature dependence of the Raman bandwidths and frequency shifts of the Eg librational mode (zero pressure) and the internal modes of ν1 and ν2 (at various pressures) for the solid nitrogen by using experimental data from the literature. Since nitrogen exhibits various solid phases and the liquid phase under the temperature and pressure conditions, it is of interest to investigate the critical behavior of the Raman bandwidths (damping constant) and the frequency shifts close to the phase transitions, particularly, transitions of α-β (Eg librational mode) and of the Ɛ-δloc–δ ( ν1 and ν2 internal modes). This then leads to explain the mechanism of the order-disorder transitions at low pressures (α-β transition) and at high pressures (Ɛ-δloc–δ transitions) in the N2 molecule.Our results are satisfactory for the Raman bandwidths (damping constant) of the librational (Eg) and the internal (ν1 and ν2 ) modes from both models (PS and EF) within the temperature and pressure ranges studied here in N2. This method of calculating the damping constant can also be applied to some other molecular solids close to phase transitions.