Unified Approach to Intensities in Vibrational Spectroscopies VIA Dynamic Electromagnetic Shieldings at the Nuclei of a Molecule

Abstract

The intensity of the radiation absorbed by a vibrating molecule can be rationalized in terms of non quantized electric Lorentz forces acting on the charged nuclei. These forces depend on the local electric field. A general expression for the effective electric field at the nuclei of a molecule in the presence of an external electromagnetic radiation, represented as a monochromatic wave, is discussed, showing that the molecular response can be described within a general framework by frequency-dependent nuclear electric and electromagnetic shielding and hypershielding tensors. It is found that the electric and electromagnetic hypershieldings are proportional to the geometrical derivatives of the dynamic dipole polarisability and of the optical rotatory power, respectively. Since intensities in Raman spectroscopy and vibrational Raman optical activity are usually interpreted in terms of these derivatives, the results demonstrate the equivalence of either description.