Dissociative single and double ionization of pyridine

Dissociative ionization processes of simple heterocyclic molecules like pyridine are relevant for an understanding of radiation damage processes in biological material that occur naturally in complex condensed environments. Pyridine can thereby be considered a simple analogue of nucleobases and related ring structures are included in many important biomolecules. We present here a detailed study of dissociative single-photon single and double ionization processes using double imaging photoelectron photoion coincidence spectroscopy, supported by quantum chemical calculations. In the case of single ionization we correlate previously described cationic states to their corresponding ionic dissociation products observed at a photon energy of 23 eV, providing additional information beyond previously reported ion appearance energies. For the case of double ionization by 36 eV photons the analysis of electron-ion-ion triple coincidences provides detailed information on the onsets of various dissociative double ionization pathways, often only different by the locations of single hydrogen atoms. The detailed understanding of dissociative single and double ionization of pyridine is a prerequisite for future studies addressing radiation damage processes of such molecules in complex environments.