Analysis of Peculiarities of the SEHRS Spectrum of - Bipyridine Molecule on the Base of the Dipole-Quadrupole Theory

TL;DR

This paper analyzes the SEHRS spectrum of 4,4' Bipyridine using Dipole Quadrupole theory, revealing strong quadrupole interactions and symmetry-related vibrational lines, and discusses the molecule's geometry and spectral features.

Contribution

It applies Dipole Quadrupole theory to interpret the SEHRS spectrum of 4,4' Bipyridine, highlighting the role of quadrupole interactions and symmetry in spectral line appearance.

Findings

Strong lines caused by vibrations with D2 symmetry

Lines from vibrations transforming as A and B1 representations

Results consistent with D2h symmetry analysis

Abstract

The SEHRS spectrum of 4,4' Bipyridine is analyzed on the base of the Dipole Quadrupole theory. It is demonstrated that there appear strong lines caused by vibrations transforming after a unit irreducible representation of the D2 symmetry group. which is most probably describes the symmetry properties of the molecule. These lines are nearly forbidden for the molecule, adsorbed on rough metal surface. Appearance of these lines is associated with a strong quadrupole light molecule interaction, which exists in this system. In addition, there are lines, caused by contributions from both the vibrations transforming after the unit irreducible representation A and the representation B1, which describes transformational properties of the dz component of the dipole moment, which is perpendicular to the surface. This result is associated with the specific geometry of the molecule, when the indicated vibrations can be nearly degenerated and cannot be resolved by the SEHRS spectra analysis. Analysis of the SEHRS spectra for the possible geometry of the molecule with the D2h symmetry group leads to similar results. This issue is in a full coincidence with the results of the SEHRS Dipole Quadrupole theory.