Sample maturation calculated using Raman spectroscopic parameters for solid organics: Methodology and geological applications

The shape and shift of Raman peak of solid organics prove to be capable of revealing atomic and molecular level vibration information of aromatic ring structure and its relationship with sample maturation. Raman “D” peaks and “G” peaks of a series of continuously maturated coal samples were measured, and the inter-peak intervals (G-D) and peak height ratios (Dh/Gh) were derived and correlated with the vitrinite reflectance (vR _o%) of standard coal samples. As a result, two formulae were established by using the two Raman indices for calculation of Raman reflectance (RmcR _o%), which is equivalent to vitrinite reflectance. The formula for calculating Raman reflectance indicative of organic maturation using Raman shift inter-peak interval (G-D) is RmcR _o%= 0.0537 d(G-D)-11.21, which is mainly applicable to matured to highly matured carbonized samples of solid organics; The formula for calculating Raman reflectance indicative of organic maturation using Raman peak height ratio (Dh/Gh) is RmcR _o%= 1.1659 h (Dh/Gh)+2.7588, which is mainly applicable to carbonized samples of solid organics that are over matured or going to be turned into granulated graphite. Preliminary applications indicate that Raman reflectance “RmcR _o %” calculated based on results of Raman spectral analysis of solid organics can be used to characterize sample maturation at molecular level, so enjoying extensive prospects in geological applications.