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Table 4
Spectral parameters or structural observables obtained from the different diagnostics.
| Spectroscopic parameter | Sample 1 | Sample 2 | Sample 3 | Meaning |
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| IR spectroscopy (“molecular” structure) | ||||
| R arom a | 0.9 | 0.5 | 0.1 | hydrogenation type |
| Apparent aromaticitiesb | 0.99 | 0.99 | 0.99 | aromatic sp2 carbon content |
| C=C/aromatic CH | medium | strong | very strong | aromatic Car/Har ratio |
| 6.2 μm band position | 6.21 | 6.29 | 6.31 | local insertion and cross-linkage of aromatic units |
| Defect band position | absent or too weak | 7.94 | 8 | Cross-linkage and/or polyaromatic units defects |
| solo/quartet | ≈1 | >1 | >1 | size of the polyaromatic units1 and/or substitution patterns |
|
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| Raman spectroscopy (carbon network) | ||||
| G band position | 1600 cm-1 | 1600 cm-1 | 1600 cm-1 | nanometer size BSU and polyaromatic units, as opposed to amorphous carbon |
| G band FWHM | 67 | 46 | 39 | Disordered sp2 carbon |
| D3 intensity | very weak or | weak | weak | Defects affecting the sp2 domains |
| absent | ||||
| AD1/(AG + AD2) | 1.51 | 2.23 | 2.59 | polyaromatic units size |
| 2*D1 bandwidth | 300 cm-1 | 256 cm-1 | 230 cm-1 | polyaromatic units size2 |
| R Tor c | 2.02 | 1.74 | 1.8 | Tortuosity and Curvature |
|
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| HRTEM images (local organisation of the carbon network) | ||||
| Size and shape of the | small (few to | small (few to | medium, approx. | primary particles sizes and shapes |
| primary particles | 15 nm), irregular | 15 nm), irregular | spherical | |
| Secondary centres | some visible | unclear | some visible | seed nuclei embedded in the primary particles |
| Soot degree of maturity | very young | very young | young | stage in the soot ageing |
| Size of the polyaromatic units | <few nm | <few nm | <few nm | size of the polyaromatic units |
| BSU | some | few | very few | organised polyaromatic domains |
| Planar, tortuous or | mainly planar | tortuous | tortuous and | shapes of the units affected by |
| fullerene-like structures | many curved | defects at the edge or within the unit | ||
| sheet | ||||
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