The Polyacetylene Raman Spectrum, Decoded

TL;DR

This paper explains the complex Raman spectral features of polyacetylene using standard spectroscopic concepts, providing insights that impact the analysis of other extended systems like graphene.

Contribution

It offers a comprehensive explanation of polyacetylene's Raman spectrum using classical concepts, clarifying previous contradictory interpretations.

Findings

Spectral features explained by band structure and phonon interactions

Raman sideband dispersion matches theoretical predictions

Implications for Raman spectroscopy of extended materials like graphene

Abstract

More than 30 years ago, polyacetylene was very much in the limelight, an early example of a conducting polymer and source of many unusual spectroscopic features spawning disparate ideas as to their origin. Several versions of the polyacetylene spectrum story emerged, with contradictory conclusions. In this paper both ordinary and peculiar polyacetylene spectral features are explained in terms of standard (if disused) spectroscopic concepts, including the dependence of electronic transition moments on phonon coordinates, Born-Oppenheimer energy surface properties, and (much more familiarly) electron and phonon band structure. Raman sideband dispersion and line shapes are very well matched by theory in a fundamental way. Most importantly, clear ramifications emerge for the Raman spectroscopy of a wide range of extended systems, including graphene and beyond, suggesting changes to some common practice in condensed matter spectroscopy.