Conferencia: Unimolecular photochemical studies of small compounds

ROSANA M. ROMANO

Mendoza

Congreso; 9th International Meeting on Photodynamics and Related Aspects; 2016

Examples of unimolecular photochemistry of small molecular compounds after irradiation of the sample with light of different energies, ranging from visible to x-ray radiation, will be presented.The excitation of a sample with visible and/or UV light usually produces conformational changes and also fragmentation of the molecule through free-radical mechanisms. These studies were performed in matrix-isolation conditions, which guarantee the study of mainly unimolecular processes. The intermediates and final products were followed by FTIR spectroscopy. This technique, in combination with theoretical calculations, is particularly well suited for the determination of conformational equilibrium, the elucidation of photochemical reaction mechanisms through the detection of reactive intermediates and free radicals and the study of intermolecular interactions or molecular complexes. The role of some of the studied molecular complexes, called ?pre-reactive? molecular complexes, in the course of a photochemical reaction will be discussed.The irradiation of the sample with more energetic photons, in the VUV and X-ray regions, produces ionization of valence or core electrons of the molecule, and the subsequent formation of a positive parent ion, which can eventually originates positive and/or neutral fragments. These studies were performed using tuneable synchrotron radiation and coincidence techniques: Photoelectron-Photoion-Coincidence (PEPICO) and Photoelectron-Photoion-Photoion-Coincidence (PEPIPI-CO). In the valence energy region the main process is the production of a single-charged molecule The fragmentation mechanisms were then followed by the detection of the positive charged fragments. In the core electron energy region, double- and, in less extent, multiple-ionization takes place. Studies of unimolecular fragmentation channels of a double-charged molecule from the shape and slope of the coincidence island of the PEPIPICO spectra will be presented.