Identical particles exchange symmetry and the electric dipole moment in molecules

TL;DR

This paper explains why molecules with identical nuclei lack permanent electric dipole moments by linking the phenomenon to the exchange symmetry of identical particles, clarifying observed spectral differences.

Contribution

It provides a fundamental symmetry-based explanation for the absence of certain spectral features in molecules with identical nuclei.

Findings

Homonuclear molecules lack permanent electric dipole moments due to exchange symmetry.

Spectral features in heteronuclear molecules are explained by symmetry considerations.

Theoretical framework connects molecular spectra with particle exchange symmetry.

Abstract

Based on fundamental symmetries, molecules cannot have a permanent electric dipole moment although it is commonly used in the literature to explain the different molecular spectra for heteronuclear and homonuclear molecules. Electric-dipole rotational and vibrational spectra can indeed be observed in heteronuclear molecules while they are missing in molecules with identical nuclei. I show that the missing spectral features can be explained as an effect of the exchange symmetry for identical particles.