Intensity ratios I_{10.0–15.2 μm}/I_{5.4–103 μm} (a), I_{10.0–15.2 μm}/I_{4.47–10.3 μm} (b), and I_{5.41–10.3 μm}/I_{4.47–5.4 μm} (c) 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 in plots (a) and (b) were drawn to guide the eye, whereas in plot (c), these lines show the exponential fitting of the data (see Appendix B for the details of the fit).