Aliphatic stretches' spectral decomposition used to calculate the methylene-to-methyl ratios. The spectra are fitted with five components corresponding to the asymmetric CH₃ stretching mode (~2960 cm⁻¹), the asymmetric CH₂ stretch and its red shoulder (~2920−2900 cm⁻¹), and the symmetric stretches of the same groups ~2880-2850 cm⁻¹). The approximate positions of these modes are labelled above the upper left spectrum. The CH₃ contributions are shown in red, and the CH₂ ones in blue. In a few spectra, a contribution from dolomite affects the profile. For these, the expected dolomite spectrum contribution is shown in brown and the dolomite-subtracted spectrum is shown above. Spectra with a high fraction of dolomite contribution were not deconvolved. In the upper right corner are shown reference spectra of linear and branched alkanes, an alkyl benzene and a cycloalkane, with varying methylene-to-methyl ratios: isocetane, squalane, n-tetradecane (purchased from Merck), and n-tetracosane (provided by Sylvie Heron) were measured as received with our FTIR-microscope; n-hexane and n-decane spectra are from Dartois et al. (2004); triethylbenzene and dimethylcyclohexane spectra are from the NIST database: https://webbook.nist.gov/chemistry/. Although they are specific species, this series shows the expected asymmetric CH₂/CH₃ stretch band ratio trend.