Raman spectroscopy can be used to study the size of the molecules that make up soot particles.
Raman spectroscopy of soot has two primary bands, the G band (~1600 cm-1) which comes from the asymmetric stretch of the inner graphitic structure of PAH and the D band. (~1350 cm-1) which is Raman active due to disorder within the plane and edges of PAH.
Using the ratio of D and G peak intensities, we can determine the conjugation length of the PAH molecules in soot particles.
For more on our work in Raman spectroscopy see our work here.