Photochemical fragmentation processes in laser ablation of organic solids

Abstract

Studies on ultraviolet (UV) laser ablation of molecular solids have received considerable attention due to its proven and potential applications. Despite its active practical use the mechanisms of laser ablation are still being studied and debated. One crucial mechanistic discussion is on the relative importance of direct photodissociation of chemical bonds versus thermal ejection following rapid conversion of light energy into heat in the ablation processes. It is generally believed that these two processes are coupled in UV ablation resulting in difficulty in analyzing the relative importance of the two mechanisms. In the simulations presented here the breathing sphere model is enhanced allowing the photon absorption event to break a bond in the molecule and then have subsequent abstraction and recombination reactions. The initial system to model is chlorobenzene. Chlorobenzene is chosen because of simplicity of its fragmentation, entailing exclusively scission of the carbon–chlorine bond to yield phenyl and chlorine radicals. The results from the simulations allow us to study the photochemical events and their coupling with the thermal processes.