Laboratory Photochemistry of Pyrene Clusters: An Efficient Way to Form Large PAHs

Abstract

In this work, we study the photodissociation processes of small PAH clusters (e.g., pyrene clusters). The experiments are carried out using a quadrupole ion trap in combination with time-of-flight (QIT-TOF) mass spectrometry. The results show that pyrene clusters are converted into larger PAHs under the influence of a strong radiation field. Specifically, pyrene dimer cations (e.g., [C 16 H 10 −C 16 H 9 ] + or C 32 H 19 + ), will photodehydrogenate and photo-isomerize to fully aromatic cations (PAHs) (e.g., C 32 H 16 + ) with laser irradiation. The structure of new formed PAHs and the dissociation energy for these reaction pathways are investigated with quantum chemical calculations. These studies provide a novel efficient evolution routes for the formation of large PAHs in the interstellar medium in a bottom-up process that will counteract the top-down conversion of large PAHs into rings and chains, and provide a reservoir of large PAHs that can be converted into C 60 and other fullerenes and large carbon cages.