A molecular dynamics study of dephasing in solid N2 and O2

Abstract

We have carried out a theoretical study of the isotropic Raman vibrational band shape in high temperature molecular solids. We employ a new vibrational exciton formalism to determine the line shape in the weak coupling limit for solids with several inequivalent lattice sites. We demonstrate that resonant vibration–vibration coupling can lead to mixing of the contributions from various lattice sites, so that it is no longer possible to associate a particular band in the spectrum with a single lattice site; the effect of V–V coupling on relative band intensities can be particularly large. We have used a molecular dynamics simulation to study the vibrational line shape of solid β-N2. The relative contributions of different parts of the potential are discussed. We have also simulated the isotropic Raman line shape of solid γ-O2, which has a lattice structure with eight molecules per unit cell in two inequivalent lattice sites. The shifts, widths, and intensities of the two Raman bands that result are calculated using an atom–atom Lennard-Jones potential and are compared with recent experiments.