The Study of Anthracene Aerosols by Solid-State NMR and ESR

The condensed solids from three aerosols resulting from heating anthracene in a drop-tube furnace with a helium atmosphere at temperatures of 1250, 1300, and 1400 K were studied by carbon-13 solid-state NMR and by ESR methods. The 1250 K sample consisted almost entirely of unreacted anthracene. However, the proton T 1 value of 17.6 s allowed the principal values of the carbon-13 chemical shift tensors to be measured by the FIREMAT experiment. The 1400 K sample appeared to be a two-component system; 9.5% (w/w) of the aerosol was extracted in dichloromethane. The extract (tar) from the 1400 K aerosol was analyzed in terms of a standard set of structural and lattice parameters. The average aromatic cluster size was found to be about 15 carbons with approximately 1.4 attachments per cluster. The NMR spectrum of the extraction residue (soot) of the 1400 K aerosol consisted of a broad featureless signal. The sample was very conductive, yielding a graphite-like factor of 0.47. The unpaired electron spin concentration was 1.2 × 1017 spins/g for the extract (tar) and 1.1 × 1020 spins/g for the residue (soot).