Intensity ratios I_{2.99–3.00 µm}/I_{2.99–3.56 µm} (a), I_{3.37–3.56 µm}/I_{2.99–3.56 µm} (b), I_{3.16–3.30 µm}/I_{2.99–3.56 µm} (c), and I_{3.37–3.56 µm}/I_{3.16–3.30 µm} (d) as a function of the n_H/n_C fraction for the flakes family (black crosses), branched family (red squares), and pretzels family (blue triangles). The dashed lines either result from the analytical data fitting (when starting below x = 0.25; see Table B1 in Appendix B for the coefficients) or were drawn to guide the eye.