Distinguishing disorder-induced bands from allowed Raman bands in graphite

The nature of the D band in the Raman spectrum of graphite has been the subject of considerable discussion. We examine the relationship between the depolarization characteristics of the D, D^', and G fundamentals and their corresponding overtones and combinations on the basal and damaged edge planes of highly oriented pyrolytic graphite in the range 800--4800 cm^-1. A clear distinction is found between the depolarization ratios of bands that are Raman allowed $(2D,$ 2D^', $2D+G)$ and those that are disorder induced $(D,$ D^', $D+G),$ implying that they are dictated by whether a Raman band is allowed in the infinite crystal, rather than by the bands' symmetry, as derived from previously proposed assignments of the D and G bands. Furthermore, although the Da/b vs 2Da/b intensity ratios could differ considerably (where $a/b=HH/VV,$ $HV/VV),$ the participation of a G phonon in the scattering process changes their value in the same amount, i.e., Da/b/D+Ga/b≈2Da/b/2D+Ga/b. Such a simple result is surprising in view of the complexity of multiphonon scattering that involves several coupled scattering events.