A deep-dive into Raman spectra of lab-produced insoluble organic matter

Meteorites, in particular carbonaceous chondrites, contain large quantities of soluble and insoluble organic matter (SOM/IOM), classified based on their solubility in solvents and acid. While much attention was given to smaller molecules such as SOM, the formation of IOM macromolecules is still an enigma. Since ice-coated dust grains are abundant in interstellar medium and protoplanetary disk, it necessitates various laboratory studies on energetic processing of icy grains to shed some light on relationships between ice, SOM, IOM and radiation. With our ICEBEAR setup, we previously demonstrated that IOM can be synthesized through heavy irradiation of simple extraterrestrial-like ice. Raman analyses of our preliminary data showed a remarkable agreement of the D- and G-band shapes recorded for the residues with data obtained from primitive carbonaceous chondrites. However, the different fitting procedures by a number of literatures resulted in variations of a standard Raman spectra. We thus attempt to refine the spectral analyses from our previous code of two Lorentzian peak-fitting to five Lorentzian peak-fitting. Our results show high degeneracy of the fitting problem due to the increase in number of free parameters and the inadequacy of physical boundary assignments to the Raman peaks. Moving forward, it is therefore necessary for the scientific community to further analyze how the D-and G- band are fitted in differentiating attributions to Raman band assignments.