Comparison of the absorption curves of soots, pitch samples and QCCs to the interstellar extinction curve

QCC (Quenched Carbonaceous Composite) is an amorphous carbonaceous material formed from a hydrocarbon plasma. In a previous paper (Sakata et al., Astrophys. J.430, 311–316, 1994), we have studied two forms of QCC: a dark QCC component located near the plasmic beam and a thermally-altered filmy QCC. Both types of QCC derivatives show an absorption feature near 217 nm, but with different extinction magnitude. A mixture of dark QCC and thermally-altered filmy QCC can explain the variations in the interstellar peak extinction. In this paper we show that soot produced from methane. methane-hydrogen gas mixtures and specially produced pitches have a broad extinction feature centered at about 217 nm. The extinction magnitude of the soots and the pitches is lower than that of the average interstellar extinction curve. We discuss the cause of the 217 nm extinction feature of soot, pitches and QCCs, and we suggest that short peripheral carbon chain structures containing π electron conjugation give rise to the 217 nm extinction feature.