Loss of a C₂H _n fragment from pyrene and circumcoronene

Abstract

Reactions at the edge of pyrene and circumcoronene are studied using the B3LYP approach in conjunction with the 4-31G and 6-31G** basis sets. The loss of a C₂H _n fragment from the edge of either molecule requires more than 7 eV, which is much larger than for the loss of an H atom. Some paths can be broken down into a series of less energetic steps, but this does not change the overall endothermicity of the process. The exception is a path where a hydrogen atom adds to pyrene or circumcoronene. The resulting molecule rearranges to have a $\hbox {C}_2\hbox {H}_2$ side group, which is subsequently lost. This process has an overall endothermicity of only about 2.5 eV. This path is actually less endothermic than the loss of an H atom from the same species.