Dipole-Quadrupole Theory of Surface Enhanced Infrared Absorption and Appearance of Forbidden Lines in the SEIRA Spectra of Symmetrical Molecules

TL;DR

This paper introduces the Dipole-Quadrupole theory for Surface Enhanced Infrared Absorption, explaining the appearance of forbidden lines in spectra of symmetrical molecules due to quadrupole interactions, supported by experimental observations.

Contribution

It proposes a new theoretical framework incorporating quadrupole interactions to explain forbidden lines in SEIRA spectra of high-symmetry molecules, expanding understanding of surface-enhanced optical phenomena.

Findings

Forbidden lines observed in SEIRA spectra of symmetric molecules.

Experimental results align with the Dipole-Quadrupole theory.

Supports development of advanced SERS and SEHRS theories.

Abstract

The paper presents main aspects of the Dipole-Quadrupole theory of Surface Enhanced Infrared Absorption (SEIRA). It is pointed out the possibility of appearance of the lines, caused by totally symmetric vibrations transforming after the unit irreducible representation, which are forbidden in usual infrared absorption spectra in molecules with sufficiently high symmetry. Observation of such lines in the SEIRA spectra of diprotonated and ethylene, adsorbed on and on mordenites is pointed out. The results well agree with our ideas about surface enhanced optical processes, based on the conception of a strong quadrupole light-molecule interaction, which allows us to develop the SERS and SEHRS theories.