Planar polycyclic aromatic hydrocarbon; found in almost pure form as the mineral pendletonite. Environmental pollutant produced as a byproduct of hydrocarbon combustion; impurity in natural carbon deposits. Possible source of infrared emission from interstellar matter. Prepn: R. Scholl, K. Meyer, Ber. 65, 902 (1932); M. S. Newman, J. Am. Chem. Soc. 62, 1683 (1940). Isoln from coal-hydrogenation oil: M. Orchin, J. Feldman, J. Org. Chem. 18, 609 (1953). UV absorption spectrum: J. W. Patterson, J. Am. Chem. Soc. 64, 1485 (1942). Photophysical properties: R. Katraro et al., Chem. Phys. 42, 121 (1979); N. Nijegorodov et al., Spectrochim. Acta A 57, 2673 (2001). Calorimetry study: Y. Nagano, J. Chem. Thermodyn. 32, 973 (2000). Quantitative structure-property relationships for polycyclic aromatic hydrocarbons: M. M. C. Ferreira, Chemosphere 44, 125 (2001). Thermodynamic properties: J. S. Chickos et al., J. Chem. Thermodyn. 34, 1195 (2002).