A Model for the Lattice Dynamics of Naphthalene and Anthracene

TLDR

Raman modes in naphthalene and anthracene do not involve rotations about the principal inertia axes. The study presents a lattice dynamics model for naphthalene and anthracene. Using a 6‑exp interatomic force model, the authors calculated dispersion curves, frequency distributions, Debye temperatures, Debye‑Waller factors, assessed their use for Raman frequencies, and computed thermal diffuse X‑ray scattering for comparison with experiment. Calculated properties agree well with experiment, except for elastic constants; low‑resolution scattering matches both experiment and difference‑Fourier theory, while high‑resolution calculations resolve earlier discrepancies.

Abstract

Abstract The lattice dynamics of a model for naphthalene and anthracene is presented. Intermolecular forces of the ‘6‐exp’ interatomic type are assumed, and dispersion curves are calculated. It is stressed that the Raman modes do not involve rotations about the principal inertia axes. Frequency distributions, Debye temperatures and Debye‐Waller factors are calculated, and the validity of using the last to estimate Raman frequencies is assessed. The agreement with experiment is good, except perhaps, for the elastic constants. Finally the thermal diffuse X‐ray scattering is calculated and compared with experiment. The low resolution results agree both with experiment and with the ‘difference Fourier transform’ theory. The high resolution calculation, however, explains the discrepancies between experiment and the earlier theory.