Selective production of soot with 216.5-224.5 nm sharp absorption feature and correlation with graphitic structure

The origin of the strong interstellar 217.5 nm absorption feature appearing in the interstellar extinction curve is a long-standing problem in astrophysics. In the present study, by a simple method, soot with sharp absorption features around 220 nm was produced from methane gas. Interestingly, it was found that the absorption peak positions of the present soot can be controlled by the production temperature. Analyzed results of soot by high-resolution electron microscope clarified that the origin of the absorption peak at 217.5 nm was a graphitic structure with a diameter of 5 nm order.