Studio sperimentale e teorico di reazioni di combustione e meccanismi di fotoionizzazione dissociativa riguardanti potenziali biocombustibili

Air pollutants arising from fossil fuels consumption are a point of major concern due to their environmental footprint and negative impact on human health. Owing to the global population growth, the demand of energy mostly based on fossil fuels is increasing rapidly, enhancing problems related with their usage. Concurrently, the decline of their limited supplies is little by little leading to a potential energy shortage, which may affect the modern lifestyle. Based on that, scientists have been working to find cleaner alternatives to replace fossil fuels. Biofuels serve the purpose, partially solving the issue related with air pollution. Nevertheless, in order to be considered as a potential biofuel, chemical-physical characteristics, as well as combustion behaviour, need to be evaluated for a chemical to be approved and definitely used in a combustion engine. In this framework, Multiplexed Photoionization Mass Spectrometry (MPIMS) has been used to study combustion-relevant reactions involving potential biofuels. Specifically, we studied the Cl-initiated oxidation reaction of diisopropyl ether (DIPE) at different temperatures (298, 550, and 650 K), and the O(3P) + 2,5-dimethylfuran (2,5-DMF) reaction at 550 K by employing a vacuum ultraviolet synchrotron radiation at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory (LBNL). Products are identified on the basis of their mass-to-charge ratio, shape of photoionization spectra, and adiabatic ionization energies. Quantum-mechanical calculations have been carried out to assess the postulated primary chemistry mechanisms accounting for products formation. Where applicable, a kinetic model has been developed to validate the potential energy surface we based on to explain the detected primary products. In particular, for the first time, the involvement of different magnetic spin surfaces has been considered to unveil the role of the intersystem crossing in interpreting the observed products. Besides that, our kinetic model suggested that in the O(3P) + 2,5-DMF reaction, primary products formation is ascribable to a non-negligible fraction of non-thermalized intermediates. Combustion environments are often depicted by kinetic modelling studies to assess the occurring set of reactions and have a general dynamic outline of the investigated system. Furthermore, photoelectron spectra are often used as fingerprints to characterize intermediates and products arising from combustion processes, and are regarded as a valuable asset to enable isomers separation and detection. Based on that, Imaging Photoelectron Photoion Coincidence Spectroscopy (iPEPICO) has been used by employing the vacuum ultraviolet beamline at the Swiss Light Source (SLS) of the Paul Scherrer Insitut (PSI) to study the dissociative photoionization behaviour of two potential biofuels, such as methyl butyrate (MB) and -valerolactone (GVL). The use of a tunable synchrotron radiation allowed for energy selection of parent ions to study their unimolecular dissociation dynamics. By plotting the fractional abundances of the detected ions at different photon energies, the so-called breakdown diagram have obtained, which has been subsequently modelled through the statistical framework given by the RRKM theory to get accurate thermodynamic data. Finally, a dynamic model simulating the time evolution of the kinetic traces of all the species deriving from alkylperoxy radicals self-reactions has been implemented. Alkylperoxy radicals arising from reactions between radical organic compounds and molecular oxygen have been found to be the precursors of different products in both combustion processes and atmospheric chemistry. This study aims at providing an insight on these products formation rate based on statistical and theoretical assumptions. Modelled kinetic traces have been compared with the experimental ones coming from MPIMS experiments.