Absolute Raman intensities of lattice modes‐investigation of intermolecular interactions in molecular crystals

Abstract

An investigation has been carried out on the correlation between intermolecular interactions and absoluteRaman intensities of lattice modes. The analysis was performed by comparing absolute Raman intensities (measured using crystalline powders) with those calculated according to the oriented-gas approximation. For the five organic compounds investigated, it could be shown that, in geoerd, the oriented-gas model is inadequate for the description of the properties of molecular crystals. Large discrepancies in the model could be revealed for modes with both librational and translational character. The discrepancies depend strongly on the strength of the intermolecular interactions.

Raman intensities of lattice vibrations in naphthalene

“…With reference to the naphthalene crystal, for instance, the effect of a rotation at site 1 can be expressed by defining the unit cell polarizability derivatives as (9) and the important quantity for the Raman intensity will be given by…”

“…In connection with the discussion to follow, it is worth noting that a basic feature of the model is that the rotation at a given site will affect the polarizability only at that site. With reference to the naphthalene crystal, for instance, the effect of a rotation at site 1 can be expressed by defining the unit cell polarizability derivatives as (9) and the important quantity for the Raman intensity will be given by…”